Liquid crystal waveguide having refractive shapes for dynamically controlling light

ABSTRACT

Liquid crystal waveguides for dynamically controlling the refraction of light. Generally, liquid crystal materials may be disposed within a waveguide in a cladding proximate or adjacent to a core layer of the waveguide. In one example, portions of the liquid crystal material can be induced to form refractive or lens shapes in the cladding that interact with a portion (e.g. evanescent) of light in the waveguide so as to permit electronic control of the refraction/bending, focusing, or defocusing of light as it travels through the waveguide. In one example, a waveguide may be formed using one or more patterned or shaped electrodes that induce formation of such refractive or lens shapes of liquid crystal material, or alternatively, an alignment layer may have one or more regions that define such refractive or lens shapes to induce formation of refractive or lens shapes of the liquid crystal material. In another example, such refractive or lens shapes of liquid crystal material may be formed by patterning or shaping a cladding to define a region or cavity to contain liquid crystal material in which the liquid crystal materials may interact with the evanescent light.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a division of U.S. patent application Ser. No.10/963,946 entitled “LIQUID CRYSTAL WAVEGUIDE HAVING REFRACTIVE SHAPESFOR DYNAMICALLY CONTROLLING LIGHT AND TUNABLE LASER INCLUDING SAME”filed Oct. 12, 2004, which claims the benefit of U.S. provisional patentapplication No. 60/539,030 filed on Jan. 22, 2004, the disclosure ofwhich is hereby incorporated by reference in its entirety.

GOVERNMENT RIGHTS

This invention was made with Government support under contract No.0319386 awarded by the National Science Foundation. The Government hascertain rights in the invention.

FIELD OF THE INVENTION

This invention relates, in general, to waveguides, and moreparticularly, to waveguides having liquid crystal materials therein.

BACKGROUND OF THE INVENTION

Various devices such as barcode scanners, compact disk players, DVDplayers, and others use light to perform various functions, such as readdata from or write data to optical media. Beams of light are also usedin communication devices, sample analyzing devices, distance measurementdevices, and time measurement devices.

Light can be controlled using standard lenses and mirrors. These passivemethods can be made active via mechanical motion. For example, mirrorscan be placed on galvo-motors to move the mirror to control thedirection of light propagation. This technique is used in barcodescanners, or optical read/write heads in CD/DVD players. However,mechanical control over light is problematic for several reasons, asrecognized by the present inventors. First, it is difficult to make suchmechanical devices compact. Second, the mechanical nature of such movingdevices have limited lifetimes due to mechanical wear and failureissues. Third, mechanical devices are inherently vibration sensitive,which limits the type of environment in which they can be used. Finally,mechanical devices necessitate a level of design complexity includinggears, bearings, and other mechanical components which add cost,expense, and maintenance issues to such designs.

Rather than move a lens or a mirror with a motor or actuator, light canbe controlled through the use of waveguides. For instance, U.S. Pat. No.5,347,377 entitled “Planar Waveguide Liquid Crystal Variable Retarder”relates generally to providing an improved waveguide liquid crystaloptical device, and discloses in Table I the use of alternating currentvoltages between 2 and 50 volts rms for retardation of the polarizedlight by controlling only the optical phase delay.

With conventional waveguides, electro-optic materials such as lithiumniobate are generally employed in the core whereby a voltage appliedacross the core material changes the index of refraction, n. However,with conventional techniques using materials such as lithium niobate,the index of refraction can only be changed a very small amount so thatthe retardation of a half wave may require thousands of volts. Thislimitation makes this type of light control extremely limited, and todate not a viable alternative to mechanical control of light.

In non-waveguide devices, liquid crystal materials have becomewidespread in display applications where light is attenuated but notsteered nor refocused. However, in order to use conventional displaytechniques for liquid crystal materials to attempt continuous steeringof light, prohibitively thick layers of liquid crystal materials(greater than 100 microns) would be needed, which would render thedevice highly opaque and slow. The thick layers of liquid crystal cantake seconds or even minutes to change, and can be difficult to control.Although non-waveguide, electro-optic beam-steerers have been made withstandard thin liquid crystal cells, such devices have only realizedminimal steering, in the range of 10⁻⁶ degrees of steering).

U.S. Pat. No. 3,963,310 entitled “Liquid Crystal Waveguide” teaches ofutilizing liquid crystal—within the core of a waveguide. However, asrecognized by the present inventors, such a waveguide would beproblematic in that there would be substantial losses or attenuation oflight traveling through such a waveguide.

Accordingly, as recognized by the present inventors, what is needed is aliquid crystal waveguide for controlling light that permits activecontrol of the propagation or refraction of light through the waveguidein a manner that provides for low loss operation.

It is against this background that various embodiments of the presentinvention were developed.

SUMMARY

In light of the above and according to one broad aspect of oneembodiment of the invention, disclosed herein is a liquid crystalwaveguide for dynamically controlling the refraction of light passingthrough the waveguide. Generally, liquid crystal materials may bedisposed within a waveguide in a cladding proximate or adjacent to acore layer of the waveguide. According to an embodiment of the presentinvention, portions of the liquid crystal material can be induced toform refractive or lens shapes in the cladding that interact with aportion (e.g. evanescent) of light in the waveguide so as to permitelectronic control of the refraction/bending, focusing, or defocusing oflight as it travels through the waveguide. In one example, a waveguidemay be formed using one or more patterned or shaped electrodes thatinduce formation of such refractive or lens shapes of liquid crystalmaterial, or alternatively, an alignment layer may have one or moreregions that define such refractive or lens shapes to induce formationof refractive or lens shapes of the liquid crystal material. In anotherexample of the invention, such refractive or lens shapes of liquidcrystal material may be formed by patterning or shaping a cladding todefine a region or cavity to contain liquid crystal material in whichthe liquid crystal materials may interact with the evanescent light.

According to one broad aspect of one embodiment of the presentinvention, a waveguide may include a core, a pair of claddingssurrounding the core wherein one of the claddings (e.g., the uppercladding) contains liquid crystal material therein. In one example, oneor more electrodes or an electrode layer is positioned above the uppercladding that has the liquid crystal material therein, and a lowerelectrode or electrode layer or plane is positioned below the lowercladding and acts as a ground plane.

The one or more upper electrodes define one or more shapes having atleast one edge or interface which is non-normal to the direction oflight propagation through the waveguide, or may define curved or lensshaped interfaces. The one or more shapes defined by the upperelectrode(s) may be used to controllably refract, bend, focus or defocuslight as light passes through the core and upper and lower claddings ofthe waveguide. The upper electrodes, also referred to herein aspatterned electrodes, may be shaped or patterned in various manners,including generally triangular or wedge shaped for steering light, orthe shapes may include various lens shapes for focusing or defocusinglight that passes through the waveguide.

When a voltage or range of voltages are applied between the upperpatterned electrode and the lower electrode, at least two indices ofrefraction can be realized within a waveguide. As voltage is applied andincreased between the upper patterned electrodes and the lower electrodeplane, the index of refraction n2 of the liquid crystal material underthe upper patterned electrodes) is controllably and dynamically changedas a function of the voltage applied.

The index of refraction n1 of the liquid crystal material that is notunder the electrode is generally not changed. In this way, thedifference between n1 and n2 can be dynamically controlled by thevoltage.

According to another broad aspect of one embodiment of the presentinvention, a waveguide may include a lower electrode plane, a lowercladding, a core layer, an alignment layer having the one or moreregions defining various shapes, an upper cladding with liquid crystalmaterial therein, an upper electrode plane, and a glass cover.

In one example on the alignment layer, one or more areas or regionsdefine various shapes in order to induce the liquid crystal material inthe adjacent upper cladding to form various shapes when no voltage isapplied, such as shapes having non-normal interfaces or shapes havingcurves or lens shapes. For instance, the alignment layer of thewaveguide may include a first region and a second region. In thisexample, the first region aligns the liquid crystal materials in theupper cladding in a first orientation (e.g., with their long axisperpendicularly orientated relative to the propagation direction oflight traveling through the waveguide); while the second region definesa refractive shape (e.g., wedge or prism shape) or lens shape, whereinwithin the second region, the liquid crystal materials in the uppercladding are aligned in a second orientation (e.g., with their long axisorientated in parallel relative to the propagation direction of lighttraveling through the waveguide).

In this example, when no voltage is applied between the upper electrodeand the lower electrode/substrate, the index of refraction n1 of thefirst region is greater than the index of refraction n2 of the secondregion for TE polarized light traveling through the waveguide. As avoltage is applied between the upper electrode and the lowerelectrode/substrate, the electric field of the applied voltage inducesthe liquid crystals within the upper cladding to orient vertically, andtherefore for TE polarized light traveling through the waveguide, theindex of refraction n1 of the first region is approximately equal to theindex of refraction n2 of the second region, and no refraction or lightbending occurs.

According to another broad aspect of one embodiment of the presentinvention, a waveguide may include a lower electrode plane, a lowercladding, a core layer, an alignment layer, an upper cladding and anupper electrode plane. In the upper cladding, regions or areas orportions have been removed to form a cavity defining one or morerefractive shapes. In one example, the cavity is filled with liquidcrystal material.

In one example, one or more cavities, areas or regions of the uppercladding have been removed or reduced and filled with liquid crystalmaterial such that the evanescent wave of the guided light may penetrateinto these areas or regions. Liquid crystal material may be placed inthese cavities or areas, such that the shape or region in which aportion of the guided light may interact with the liquid crystal definesrefractive shapes having non-normal interfaces or refractive shapeshaving curves or lens shapes. For instance, the upper cladding of thewaveguide may include a first region and a second region, wherein thefirst region may include a non-electro-optic upper cladding material;and while the second region defines a refractive shape (e.g., wedge orprism shape) or lens shape, wherein within the second region, there isliquid crystal material therein such that the evanescent wave mayinteract with the liquid crystal material in this second region.

In one example, when no voltage is applied between the upper electrodeand the lower electrode, the index of refraction n1 of the first regionis different than the index of refraction n2 of the second region forlight traveling through the waveguide. As a voltage is applied betweenthe upper electrode and the lower electrode, the electric field of theapplied voltage induces the liquid crystals, which are confined withinthe regions or cavities of the upper cladding, to reorient, andtherefore for light traveling through the waveguide, the differencebetween the index of refraction n1 of the first region and the index ofrefraction n2 of the second region will change, and therefore the degreeof refraction or light bending will also change.

According to another broad aspect of an embodiment of the presentinvention, disclosed herein is a method for dynamically controllingrefraction of a light beam through a waveguide having a core and atleast one cladding. In one example, the method may include providing aliquid crystal material within the at least one cladding; providing forforming at least one refractive shape from the liquid crystal materialin the at least one cladding; providing at least one alignment layeradjacent the core, the alignment layer inducing a substantially uniformarrangement of the liquid crystal material of the at least onerefractive shape; and providing for passing the light beam through thewaveguide, wherein an evanescent portion of the light beam interactswith the at least one refractive shape having the substantially uniformarrangement of the liquid crystal material, thereby reducing attenuationof the light beam as it travels through the waveguide.

In one example, the at least one cladding may include an upper and lowercladding, and the operation of providing a liquid crystal material maycomprise providing the liquid crystal material in the upper cladding orin the lower cladding.

In another example, the operation of providing for forming at least onerefractive shape may comprise providing for applying an electric fieldto a portion of the liquid crystal material, thereby inducing theportion of the liquid crystal material to form at least one refractiveshape; providing at least one electrode for receiving at least onevoltage; forming the electrode to include at least one refractive shape;and providing for applying a voltage to the electrode thereby inducingthe portion of the liquid crystal material to form at least onerefractive shape.

In one example, the at least one refractive shape may have a variableindex of refraction, and the method may comprise providing for varyingthe electric field, thereby adjusting the variable index of refractionof the at least one refractive shape; and providing for varying thevoltage applied to the electrode in order to adjust an index ofrefraction of the at least one refractive shape.

In another example, the operation of providing for forming at least onerefractive shape may comprise providing at least one alignment layeradjacent at least one cladding; forming the alignment layer to have atleast a first region biasing the liquid crystal material in a firstorientation, and the alignment layer may have a second region biasingthe liquid crystal material in a second orientation, the second regionmay define at least one refractive shape; providing at least oneelectrode for receiving at least one voltage, the electrode may define aplane; and providing for applying a voltage to the electrode, therebyre-orienting the liquid crystal material in the at least one cladding.

In one example, the first region may have a first index of refractionand the second region may have a second index of refraction, and themethod may comprise providing for varying the voltage applied to theelectrode in order to adjust a difference between the first and secondindex of refraction.

In one example, the operation of providing for forming at least onerefractive shape may comprise forming a cavity in the at least onecladding, the cavity may define at least one refractive shape; placingthe liquid crystal material in the cavity; and providing for applying anelectric field to the cavity, thereby re-orienting the liquid crystalmaterial in the cavity. In another example the liquid crystal materialin the cavity may have an index of refraction, and when the electricfield is applied to the cavity, the index of refraction of the liquidcrystal material in the cavity may change, thereby altering an amount ofrefraction of the light beam in the waveguide.

In one example, the operation of providing for applying an electricfield may comprise providing at least one electrode for receiving atleast one voltage, the electrode may define a plane; and providing forapplying a voltage to the electrode. In another example, the operationof forming a cavity may comprise shaping the cavity to include at leastone wedge shape or at least one lens shape.

According to another broad aspect of an embodiment of the presentinvention, disclosed herein is a waveguide for controllably refracting alight beam. In one example, the waveguide may comprise a core forguiding a light beam through the waveguide, and a means for controllablyrefracting the light beam as it travels through the waveguide.

In another example, the means for controllably refracting may include atleast one cladding having a liquid crystal material therein; at leastone electrode for receiving at least one voltage, the electrode maydefine at least one refractive shape, wherein the light beam isrefracted by an amount that is controlled by the at least one voltage.

In one example, the means for controllably refracting may include atleast one cladding having a liquid crystal material within at least aportion of the cladding wherein at least a portion of the liquid crystalmaterial forms one or more refractive shapes having an index ofrefraction; and at least one electrode, wherein as a voltage is appliedto the electrode, the index of refraction of the one or more refractiveshapes is altered to controllably refract the light beam as it travelsthrough the waveguide.

In another example, the means for controllably refracting may include atleast one cladding having a liquid crystal material disposed therein,the cladding may have a first region characterized by a first index ofrefraction and a second region characterized by a second index ofrefraction; and at least one electrode, wherein at least the secondindex of refraction is controlled by a voltage applied to the electrode.

In another example, the means for controllably refracting may include atleast one cladding may have a liquid crystal material disposed therein,the cladding may have at least a first region that includes at least aportion of the liquid crystal material having a first orientation; andat least one electrode, wherein the first orientation of the firstportion of the liquid crystal material in the at least first regionselectively changes from a first state to a second state based on avoltage applied to the electrode.

Other features, utilities and advantages of the various embodiments ofthe invention will be apparent from the following more particulardescription of embodiments of the invention as illustrated in theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example of a waveguide having a patternedelectrode for providing active control of light propagation, inaccordance with an embodiment of the present invention.

FIG. 2 illustrates a sectional view taken along section lines 2-2 ofFIG. 1, illustrating an example of an embodiment of the presentinvention.

FIG. 3 illustrates an example of operations for forming a waveguidehaving patterned electrodes for controlling light, in accordance with anembodiment of the present invention.

FIG. 4 illustrates a sectional view of the waveguide along section lines4-4 of FIG. 1 where no voltage is applied to the patterned electrode, inaccordance with one embodiment of the invention.

FIG. 5 illustrates a top view of the liquid crystals as oriented in theupper cladding of FIG. 4 where no voltage is applied to the patternedelectrode, in accordance with one embodiment of the present invention.

FIG. 6 illustrates a sectional view of the waveguide along section lines4-4 of FIG. 1, wherein a voltage is applied to the patterned electrodeso as to alter the orientation of the liquid crystal material under thepatterned electrode, in accordance with one embodiment of the presentinvention.

FIG. 7 illustrates a top view of the liquid crystal material in theupper cladding of FIG. 6, when a voltage is applied to the patternedelectrode, in accordance with one embodiment of the present invention.

FIG. 8 illustrates a sectional view of the waveguide along section lines4-4 of FIG. 1 where no voltage is applied to the patterned electrode, inaccordance with one embodiment of the present invention.

FIG. 9 illustrates a top view of the liquid crystal material within theupper cladding of the waveguide of FIG. 8 where no voltage is applied tothe upper electrode, in accordance with one embodiment of the presentinvention.

FIG. 10 illustrates a sectional view of the waveguide of FIG. 1 takenalong section lines 4-4, when a voltage is applied to the patternedelectrode so as to change the orientation of the liquid crystal materialunder the patterned electrode, in accordance with one embodiment of thepresent invention.

FIG. 11 illustrates a top view of the liquid crystal material within theupper cladding of FIG. 10 when a voltage is applied to the patternedelectrode, in accordance with one embodiment of the present invention.

FIG. 12 illustrates an alternative embodiment of the present inventionwherein a patterned electrode is positioned between the substrate andthe lower cladding of a waveguide, in accordance with one embodiment ofthe present invention.

FIG. 13 is a sectional view of a waveguide taken along section 13-13 ofFIG. 12, in accordance with one embodiment of the present invention.

FIG. 14 illustrates an example of operations for forming a waveguidehaving one or more patterned electrodes for controlling the propagationof light through the waveguide, in accordance with one embodiment of thepresent invention.

FIG. 15 illustrates an example of a patterned electrode for controllinglight propagating through a waveguide, in accordance with an embodimentof the present invention.

FIG. 16 illustrates another example of a patterned electrode forcontrolling light propagating through a waveguide, in accordance with anembodiment of the present invention.

FIG. 17 illustrates an example of a pair of patterned electrodes forcontrolling light propagating through a waveguide, in accordance with anembodiment of the present invention.

FIG. 18 illustrates another example of a pair of patterned shapedelectrodes for controlling light propagating through a waveguide, inaccordance with an embodiment of the present invention.

FIG. 19 illustrates another example of a patterned electrode forcontrolling light propagating through a waveguide, in accordance with anembodiment of the present invention.

FIG. 20 illustrates an example of operations for forming a waveguidehaving one or more electrodes with curved or lens shaped interfaces forcontrolling the propagation of light through the waveguide, inaccordance with one embodiment of the present invention.

FIG. 21 illustrates an example of an electrode formed in the shape of asimple positive lens for controlling light propagating through awaveguide, in accordance with one embodiment of the present invention.

FIG. 22 illustrates an example of an electrode formed in the shape of anegative lens for controlling light propagating through a waveguide, inaccordance with one embodiment of the present invention.

FIG. 23 illustrates an example of an electrode formed in the shape of aconvex-convex lens for controlling light propagating through awaveguide, in accordance with one embodiment of the present invention.

FIG. 24 illustrates an example of an electrode formed in the shape of aconcave-concave lens for controlling light propagating through awaveguide, in accordance with one embodiment of the present invention.

FIG. 25 illustrates an example of an electrode formed in the shape of aconvex-concave lens for controlling light propagating through awaveguide, in accordance with one embodiment of the present invention.

FIG. 26 illustrates an example of an electrode formed in the shape of aconcave-concave asphere lens for controlling light propagating through awaveguide, in accordance with one embodiment of the present invention.

FIG. 27 illustrates another example of an electrode for controllinglight propagating through the waveguide, in accordance with oneembodiment of the present invention.

FIG. 28 illustrates an alternative embodiment wherein the waveguideutilizes an alignment layer having two or more areas or regions havingdifferent orientations that align the liquid crystal material in theadjacent cladding so as to form refractive shapes within the liquidcrystal material in the cladding for controlling light propagatingthrough a waveguide, in accordance with one embodiment of the presentinvention.

FIG. 29 illustrates a sectional view of the waveguide of FIG. 28 takenalong section lines 29-29 with no voltage applied, in accordance withone embodiment of the present invention.

FIG. 30 illustrates a sectional view of the waveguide of FIG. 28 takenalong section lines 29-29 with a voltage applied, in accordance with oneembodiment of the present invention.

FIG. 31 illustrates a top view of the liquid crystals within the uppercladding of the waveguide of FIG. 28 when no voltage is applied, inaccordance with one embodiment of the present invention.

FIG. 32 is a top view of the liquid crystal material within the uppercladding of the waveguide of FIG. 28 when a high voltage is applied soas to re-orient the liquid crystal material therein, in accordance withone embodiment of the present invention.

FIG. 33 illustrates an example of operations for forming a waveguidehaving two or more areas or regions having different orientations thatalign the liquid crystal material in the adjacent cladding so as to formrefractive shapes within the liquid crystal material for controllinglight propagating through a waveguide, in accordance with one embodimentof the present invention.

FIG. 34 illustrates an alternative embodiment wherein the waveguideutilizes an upper cladding layer having a first region and a secondregion, the second region including a cavity having liquid crystalmaterial therein, the cavity defining one or more refractive shapes forcontrolling light propagating through a waveguide, in accordance withone embodiment of the present invention.

FIG. 35 illustrates a sectional view of the waveguide of FIG. 34 takenalong section lines 35-35 with no voltage applied, in accordance withone embodiment of the present invention.

FIG. 36 illustrates a sectional view of the waveguide of FIG. 34 takenalong section lines 35-35 with a voltage applied, in accordance with oneembodiment of the present invention.

FIG. 37 illustrates a top section view of the upper waveguide claddingof the waveguide of FIG. 34, which contains a first region withoutliquid crystals and a second region with liquid crystals, when novoltage is applied, in accordance with one embodiment of the presentinvention.

FIG. 38 illustrates a top section view of the upper waveguide claddingof the waveguide of FIG. 34, which contains a first region withoutliquid crystals and a second region with liquid crystals, when a highvoltage is applied, in accordance with one embodiment of the presentinvention.

FIG. 39 illustrates an example of operations for forming a waveguidehaving a cladding with at least a first and second region, the secondregion having a cavity with liquid crystal material therein, the cavitydefining one or more refractive shapes within the upper cladding forcontrolling light propagating through a waveguide, in accordance withone embodiment of the present invention.

FIG. 40 illustrates an example of a barcode scanner utilizing awaveguide having a plurality of patterned electrodes for controllinglight, in accordance with an embodiment of the present invention.

FIG. 41 illustrates an example of an electrode formed in the shape ofbus bars with multiple connection points, wherein application ofvoltages at the three connection points enables control of voltagegradients across the electrode in accordance with one embodiment of thepresent invention.

FIG. 42 illustrates a sectional view of the waveguide with the electrodeof FIG. 41, when no voltage is applied to the electrode, in accordancewith one embodiment of the present invention.

FIG. 43 illustrates a sectional view of the waveguide with the electrodeof FIG. 41, when a voltage is applied to the electrode so as to changethe orientation of the liquid crystal material under the electrode, inaccordance with one embodiment of the present invention.

FIG. 44 illustrates a sectional view of the waveguide with the electrodeof FIG. 41, when a plurality of differing voltages are applied to thedifferent connection points of the electrode so as to change theorientation of the liquid crystal material under the electrode, inaccordance with one embodiment of the present invention.

FIG. 45 illustrates a perspective view of an optical read/write head fora CD/DVD player including a waveguide having a plurality of patternedelectrodes for controlling light, in accordance with an embodiment ofthe present invention.

FIG. 46 illustrates a top view of the optical read/write head of FIG. 41with related circuitry, in accordance with an embodiment of the presentinvention.

DETAILED DESCRIPTION

Disclosed herein are various embodiments of a waveguide for dynamicallycontrolling the refraction of light passing through the waveguide.Generally and in accordance with an embodiment of the present invention,liquid crystal materials may be disposed within a waveguide in acladding proximate or adjacent to a core layer of the waveguide.Portions of the liquid crystal material in the cladding can be inducedto form refractive shapes or lens shapes in the cladding so as to permitelectronic control of the refraction/bending, focusing, or defocusing oflight as it travels through the waveguide. As disclosed herein, awaveguide may be formed using one or more patterned or shaped electrodesthat induce the liquid crystal material in the cladding to form suchrefractive or lens shapes (see FIGS. 1-27); an alignment layer may haveone or more regions that define such refractive or lens shapes andinduce the liquid crystal material in the cladding to form (see FIGS.28-33); or a cladding may have a cavity, region or area defining arefractive or lens shape with liquid crystal material therein in whichthe liquid crystal material interacts with the guided light may be (seeFIGS. 34-39). Various embodiments of the present invention are describedherein.

As shown in FIG. 1, in one example, a waveguide 50 may include a core52, a pair of claddings 54, 56 surrounding the core 52 wherein one ofthe claddings (e.g., the upper cladding 54) contains liquid crystalmaterial 58 therein. In one example, one or more electrodes or anelectrode layer 60 is positioned above the upper cladding 54 that hasthe liquid crystal material 58 therein, and a lower electrode orelectrode layer or plane 62 is positioned below the lower cladding 56and acts as a ground plane.

The one or more upper electrodes 60 define one or more shapes having atleast one edge or interface 64 that is non-normal to the direction oflight propagation 66 through the waveguide 50. As discussed below, theone or more shapes defined by the upper electrode(s) 60 may be used tocontrollably refract or bend light as light passes through the core 52and upper and lower claddings 54, 56 of the waveguide. The upperelectrodes 60, also referred to herein as patterned electrodes, may beshaped or patterned in various manners, including generally triangularor wedge shaped for steering light, or the shapes may include variouslens shapes for focusing or defocusing light that passes through thewaveguide 50.

In general and as discussed below, at least two indices of refractioncan be realized within a waveguide made according to embodiments of thepresent invention. The liquid crystal material 58 which is not beneaththe patterned electrodes(s) 60 may be characterized as having a firstindex of refraction n1, and n1 is generally unaffected by theapplication of a voltage 68 to the patterned electrodes 60.

The liquid crystal material 58 beneath the patterned electrodes 60 canbe characterized as having a tunable and dynamic index of refraction n2.In one example, when no voltage 68 is applied to the upper electrode 60,n2 equals n1 and no refraction occurs. As voltage 68 is applied andincreased between the upper patterned electrode(s) 60 and the lowerelectrode plane 62, the index of refraction n2 of the liquid crystalmaterial under the upper patterned electrode(s) 60 is controllablychanged as a function of the applied voltage 68. Depending upon theimplementation, the applied voltage 68 can be a DC voltage, or an ACvoltage, for instance, at low frequencies to high frequencies such as 50KHz or higher.

Hence, as the difference between n2 and n1 increases, the amount ofrefraction or bending of light passing through the waveguide 50 can beincreased as well. Hence, the amount of bending or refraction of lightas it passes through the waveguide 50 can be controlled electronicallyand without any moving parts to perform numerous useful functions, suchas for use in a barcode scanner, a CD/DVD read/write head, a tunablelaser, or other applications. In FIG. 1, the input light beam is shownas 66, and the output light beam is shown as 70, with the amount ofoutput angle of output light beam 70 being a function of the appliedvoltage 68, among other things.

As shown in FIG. 1, the waveguide 50 may be generally rectangular inshape and may include a core 52 having a generally rectangularcross-section or defining a parallel piped between walls 72. On thefront end 74 of the waveguide 50, light 66 is introduced into thewaveguide core 54 and propagates along the length of the waveguide 50 tothe distal end 76 of the waveguide 50. As shown in FIG. 1, the directionof propagation of light 66 through the waveguide 50 is generally alongthe length of the waveguide 50, and use of embodiments of the presentinvention permit the output propagation direction or angle 70 to becontrollably altered depending, in part, on the shapes of the upperelectrodes 60 and the voltages 68 applied between the upper electrodes60 and the lower electrode or plane 62. Although the waveguide 50 inFIG. 1 is shown as generally rectangular, it is understood that awaveguide made according to one or more embodiments of the presentinvention could have other shapes such as square, trapezoid,parallelogram, any polygon, or even be diced or scribed so as to haverounded edges producing elliptical, circular, or any curved shape.

As shown in FIGS. 1-2, 4, 6, 8, 10 and others, the core 52 may be asubstantially planar core that can define a substantially planar upperand/or lower surface that may extend or span the length, or a portion ofthe length, of the waveguide 50. In one example, the light beam 66 isrefracted or steered in a direction parallel to the substantially planarupper or lower surface of the core 52. In another example, therefraction of the light beam 66 is confined to be in a directionsubstantially parallel to the upper or lower planar surface of the core52. In another example, the upper and/or lower substantially planarsurface of the core 52 may be parallel to the electrodes 56, 60 in thewaveguide 50.

In one example, the patterned electrode(s) 60 may include a tab orextension therefrom 78 which permits the patterned electrode(s) to beelectrically connected to other electrical elements, such as a voltagesource 68 coupled between the patterned electrode 60 and the lowerelectrode or plane 62. Alternatively, electrical traces, conductors,vias or other conventional connection types may be utilized instead ofor with tab 78 to electrically couple a patterned electrode 60 to otherelectrical elements.

FIG. 2 illustrates a sectional view of a waveguide 50 in accordance withone embodiment of the present invention. As shown in FIG. 2, in oneexample, a waveguide 50 may include a substrate 80 such as a P-dopedsilicon substrate or any other conductive material, which providesstructural support for the waveguide 50 and also acts as a lowerelectrode or ground plane 62 to which a voltage 68 may be applied. Thesubstrate 80 may also be formed from any metal, such as silver, copper,aluminum, gold, titanium, etc. Alternatively, the substrate 80 can benonconductive, such as a glass or crystal, and a conductive coating orelectrical ground plane can be applied to the top of the substratesurface, between the substrate 80 and lower cladding 56. This conductivecoating can be ITO, Au, Ag, Al, Cu, or any other of a number ofconductive coatings. If the substrate 80 is constructed from Si, thencircuitry can be directly integrated into the substrate 80 if desired.The conductive substrate 80 is also referred to herein as the lowerelectrode 62.

A lower cladding layer 56 is provided on the substrate 80 and ispreferably made of any dielectric materials with low absorptions whoseindex of refraction is less than the index of refraction of the core.Suitable materials include Silicon OxyNitride, Silicon-Rich Nitride,Silicon Nitride, Tantalum Pentoxide, Polymers, Pure Silicon, Ionexchange glass on substances such as Lithium Niobate, Sol-Gel, thermallyoxidized silicon, glass. In one example, the interface between the lowercladding 56 and the core layer 52 is transparent so that light canpenetrate the lower cladding 56 as it propagates through the core 52.

On top of the lower cladding 56, a waveguide core or core material 52 isprovided. In one embodiment, the core 52 does not include any liquidcrystal material 58 therein. The core 52 may be made of materials suchas any dielectric materials with low absorptions whose index ofrefraction is greater than the index of refraction of the upper andlower claddings 54, 56. Suitable materials include, but are not limitedto, Silicon OxyNitride, Silicon Rich Nitride, Silicon Nitride, TantalumPentoxide, Polymers, Pure Silicon, Ion exchange glass on substances suchas Lithium Niobate, Sol-Gel, thermally oxidized silicon, glass. In oneexample, the core 54 has a thickness that is tapered or includes achannel. Furthermore, a core 54 may have a constant index of refractionalong the length of the waveguide 50, or alternatively have an index ofrefraction that varies across or along the device.

On top of the core layer 52, an alignment layer 82 (shown as the loweralignment layer 82 in this example) is provided which is used toinitially align or bias the orientation of liquid crystal material 58that is proximate to or adjacent to the alignment layer 82 and the core52. Alignment can be achieved, for example, by buffed polyimide, nylon,or other polymer coating applied to the core 52 and or the cover plate84, photo-aligned polyimide, polymer or other photo-aligned material,angle deposited SiO, SiO2 or other angle deposited material,microgrooves etched or directly e-beam written into the core 52 and orcover plate 84, ion-buffed surfaces on the core or lower cladding, adispersed polymer matrix that is photoaligned, or direct buffing ofeither surface. In one example the alignment layer 82 may be a coatingor layer that induces a homeotropic alignment in the liquid crystal 58.In one example, the lower alignment layer 82 is generally transparent.

On top of the lower alignment layer 82, the upper cladding 54 isprovided having liquid crystal material therein 58. In one example, theinterface between the lower alignment layer 82 and the upper cladding 54is transparent. The liquid crystal material 58 may include, but is notlimited to, any nematic liquid crystal, with either a positivedielectric constant or a negative dielectric constant or a mixture ofeach, polymer dispersed liquid crystal material, Smectic A* and C*liquid crystal material, cholesteric liquid crystal material such asferroelectrics and surface stabilized ferroelectrics, or dual-frequencyliquid crystal material, for example. While the various figures hereinshow the liquid crystal material 58 as being nematic liquid crystal, itis understood that embodiments of the present invention may utilizeother types of liquid crystal material.

In one example, the upper cladding 54 is formed using spacer material todefine a region or volume wherein liquid crystal material 58 may becontained therein, and optically transparent glue such as Norland 68 maybe used to create transparent boundary walls 72 to contain the liquidcrystal 58.

On top of the upper cladding 54, an upper alignment layer 86 may beprovided to initially align or bias the orientation of liquid crystalmaterial 58 that is adjacent to or proximate to the upper alignmentlayer 86. As with the lower alignment layer 82, alignment can beachieved, for example, by buffed polyimide coating, photo-alignedpolyimide, angle deposited SiO and or SiO2, microgrooves etched orotherwise formed, ion-buffed surfaces, a dispersed polymer matrix thatis photoaligned, or direct buffing. In one example, the upper alignmentlayer 86 is generally transparent.

The alignment of the liquid crystal 58 between the lower and upperalignment layers 82, 86 can be anti-parallel, parallel, twisted, orhybrid between twisted and parallel or anti-parallel. The direction ofliquid crystal alignment can be at any angle with respect to thedirection of light propagation 66. Described below are examples of wherethe alignment of the liquid crystal materials 58 is adapted to providefor refraction of TE or TM modulated light as it passes through awaveguide made according to embodiments of the present invention.

On top of the upper alignment layer 86 and below the glass cover 84, apatterned electrode layer 60 or portions of the patterned electrodelayer 60 are present. In one embodiment, the patterned electrode layer60 includes one or more electrodes having non-normal interfaces 64relative to the orientation of light 66 traveling through the waveguide50, or includes one or more curved or lens shaped interfaces 64. In oneexample, the patterned electrode layer 60 is a conductive coatingapplied to the bottom surface of the glass cover 84. The conductivecoating can include, but is not limited to, ITO, Au, Ag, Al, Cu, or anyother conductive coating. In another example, the patterned electrode 60can be p-doped silicon or any metal, such as silver, copper, aluminum,gold, titanium, alloys, or other conductive material, etc. In oneexample, the glass cover 84 may be made of materials such as, but notlimited to, standard float glass such as Corning 1737, fused silica, orany flat surface. Since the evanescent portion of the light preferablydoes not pass through the cover plate 84, the cover plate 84 can be madefrom non-transparent materials such as silicon wafers, ceramics, orpolished metal surfaces. In another embodiment, the cover plate 84 maybe a metal or any other conductive material and serve as the upperelectrode.

Using the structure of FIGS. 1-2 or variations thereof, variousdifferent waveguides 50 can be formed to selectively and controllablyrefract, bend, or focus light 66 as it passes through the waveguide 50.When a voltage 68 is applied between the patterned electrode(s) 60 andthe substrate 80, an electric field is formed between the patternedelectrode 60 and the substrate 80 which induces movement of the liquidcrystals 58 in the upper cladding 54 that are subject to the appliedelectric field. As the liquid crystals 58 move or change theirorientation based on the applied voltage, the index of refraction of theaffected portion of the upper cladding 54 is changed relative to theindex of refraction of the non-affected portions of the liquid crystalmaterial 58 in the upper cladding 54. As shown in FIG. 1, the portion ofthe waveguide 50 which is not affected by the electric field createdbetween the patterned electrode 60 and the substrate 80 can becharacterized as having a first index of refraction (shown as n1), whilethe portion of the waveguide 50 affected by the electric field createdbetween the patterned electrode 60 and the substrate 80 may becharacterized as having a second index of refraction (shown as n2).Under Snell's Law, light refracts when crossing an interface 64 betweentwo different indices of refraction if the interface 64 is oriented in anon-normal relation to the direction of propagation of light 66. In FIG.1, the patterned electrode 60 has a non-normal interface 64 on itsdistal trailing edge, so that as light 66 propagates through thewaveguide 50 from the front end 74 to the distal end 76 of the waveguide50, light 66 is refracted or steered (shown as 70) in a controlledmanner depending upon the amount of voltage 68 applied between thepatterned electrode 60 and the substrate 80.

Preferably, the core layer 52 is surrounded by an upper and lowercladding 54, 56, wherein the interfaces between the lower cladding 56and the core layer 52 and between the upper cladding 54 and the corelayer 52 are transparent. As light 66 enters the core layer 52 andpropagates through the core 52 along the length of the waveguide 50, theevanescent portion of the propagating light 66 waves penetrates intoboth the upper and lower cladding 54, 56. Preferably, the core layer 52has a fixed index of refraction, and the lower cladding also has a fixedindex of refraction. By providing liquid crystal material 58 within theupper cladding 54, a portion of which is controllably subjected to anelectric field between the patterned electrode 60 and the substrate 80,the index of refraction (n2) of the upper cladding layer 54 can becontrollably altered. Stated differently, the average index ofrefraction (also referred to herein as the effective index ofrefraction, or index of refraction) of the upper cladding 54, core 52,and lower cladding 56 as experienced by a single TN or TE mode of lightin the waveguides can be controllably altered by altering the index ofrefraction (n2) of the upper cladding 54. Hence, as light 66 passesthrough the waveguide core 52 and upper and lower cladding 54, 56, thelight 66 can be controllably refracted, steered, or focused (70) throughthe use of the upper electrode 60 having a non-normal interface 64therein. Because the liquid crystal material 58 is disposed within theupper cladding 54 and interacts primarily with the evanescent portion ofthe light wave 66 and the fundamental portion of the light wave 66passes through the core material 52, there is no significant attenuationof the intensity of the light 66 as the light 66 passes through thewaveguide 50. This permits the length of the waveguide 50 to bebeneficially long so that numerous electrodes 60 can be utilized in acascade or series arrangement if desired, for example as in FIGS. 16-18.

Furthermore, in one example, the evanescent portion of the light 66 isonly interacting with the liquid crystal molecules 58 that are close tothe alignment layer 82. These molecules 58 are more highly ordered thanliquid crystal molecules 58 further away from the alignment layer 82 andtherefore scatter less light. In one example, the losses aresufficiently low (e.g., less than 0.5 dB/cm) that the waveguide 50length can be lengthy (e.g., 4 inches or greater).

In one embodiment of the invention, a waveguide 50 may be formed havinga first and second assembly 90, 92, wherein the first and secondassemblies 90, 92 are attached to one another in order to form theoverall waveguide 50. As shown in FIG. 2, the first assembly 90 mayinclude the substrate 80, the lower cladding 56, the core 52, and thelower alignment layer 82; and the second assembly 92 may include theglass cover 84, the patterned electrode(s) 60, the upper alignment layer96 and upper cladding 54 with liquid crystal material 58 therein. Onemethod for forming a waveguide is illustrated below in FIGS. 3 and 14.

While FIGS. 1-2 show a particular arrangement of layers of a waveguideaccording to one embodiment of the present invention, it is understoodthat the present invention contemplates variations of this arrangement.For instance, the patterned electrode(s) 60 may be positioned in adifferent layer than as shown in FIG. 1-2, such as proximate the lowerportion of the waveguide 50 (see FIG. 12 as an example). The conductivelower electrode 62 may also be positioned at different layers within thewaveguide if desired. Further, while two alignment layers 82, 86 areshown, the invention may include a single alignment layer. While theliquid crystal material 58 is shown as disposed within the uppercladding 54, it is understood that the liquid crystal material 58 may bedisposed in the lower cladding 56 if desired.

FIG. 3 illustrates an example of operations 100 for controlling therefraction of light through a waveguide, in accordance with oneembodiment of the present invention. At operation 102, the waveguide isprovided with a core, an upper cladding, and a lower cladding where inone example the upper cladding has liquid crystal material disposedtherein. Alternatively, liquid crystal material may be disposed withinthe lower cladding if desired. At operation 104, one or more electrodesare provided for controlling the orientation of the liquid crystalmaterial proximate the one or more electrodes, wherein the one or moreelectrodes have at least one non-normal interface relative to thedirection of propagation of light through the waveguide. As discussedabove, the non-normal interface results in refraction, steering, orbending of light as light exits the non-normal interface. At operation106, a second electrode or ground plane is provided. In one example, asubstrate material of the waveguide is electrically conductive and actsas a lower electrode or ground plane so that a controlled voltage can beapplied between the patterned electrode and the substrate to create anelectric field therebetween.

At operation 108, at least one alignment layer is provided to align theliquid crystal material proximate the core. For instance, a loweralignment layer (such as 82 in FIG. 2) can be provided to initiallyalign or bias the liquid crystals within the upper cladding and adjacentto the lower alignment layer. By providing the alignment layer, theliquid crystal material responds to an applied voltage in a faster andmore orderly and predictable manner. Further, when no voltage is appliedto the liquid crystal material, the alignment layer provides sufficientliquid crystal ordering to minimize scattering of the light propagatingthrough the waveguide because the evanescent portion of the lightinteracts primarily with the highly ordered liquid crystal moleculesalong the alignment layer.

At operation 110, the introduction of light is provided into thewaveguide core such that as the primary or fundamental portion of thelight input into the waveguide travels through the core, and theevanescent portion of the light passes through the upper and lowercladdings of the waveguide. In one example, operation 110 is achieved byprism coupling, grating coupling, end-fire coupling or otherconventional coupling techniques. In another embodiment, polarized light(such as TE or TM polarized light) is introduced into the waveguide andoperation 108 provides a liquid crystal orientation that is adapted tocontrollably refract, steer, or focus the polarized light.

At operation 112, a voltage is applied between the one or moreelectrodes and the lower electrode in order to change the effectiveindex of refraction of the materials between the one or more electrodesand the lower electrode. By altering the refraction of the liquidcrystal material under the patterned electrodes (e.g., shown as n2 inFIG. 1), a modulation index or change in the index of refraction(referred to as ΔN) is achieved. As the modulation index ΔN increases,the amount of light beam refraction also increases, which permitsactive, solid state control of the amount of refraction of light passingthrough the waveguide. At operation 114, the amount of applied voltagemay be altered to controllably refract or bend the light travelingthrough the waveguide.

In one example of waveguides formed in accordance with embodiments ofthe present invention, various degrees of modulation index throughwaveguides were achieved, and are summarized in Table 1 and Table 3.Hence, it can be seen that by the operations of FIG. 3, light can becontrollably refracted or steered as it passes through a waveguide.

Embodiments of the present invention can be used to selectively controlthe index of refraction for particular types of polarized light, such asTM polarized light and TE polarized light. Generally, TM (TransverseMagnetic) polarized light means that the magnetic field of the lightwave is traversing the plane of the waveguide, while the electric fieldis substantially perpendicular to the plane of the waveguide. TE(Transverse Electric) polarized light is characterized by the electricfield of the light traversing the plane of the waveguide, while themagnetic field of the light is substantially perpendicular to the planeof the waveguide.

FIGS. 4-7 and 8-11 illustrate various examples of how embodiments of thepresent invention may be used to refract, steer, or focus light that hasbeen polarized either as TE or TM polarization. Referring to FIGS. 4-7,if the liquid crystals 58 disposed within the upper cladding 54 areinitially aligned (e.g., through the use of the lower and upperalignment layers 82, 86) in such a way that the long axis of the liquidcrystals 58 are aligned in parallel with the direction of lightpropagation 66 through the waveguide 50 (FIGS. 4-5 show this situationwhen no voltage 68 is applied to the electrodes 60, 62), then whenvoltage 68 is applied to the electrodes 60, 62, the liquid crystals 120beneath the patterned electrode 60 respond by rotating upwardly in aplane containing the applied electric field vector and the propagationvector of the light 66. The liquid crystals 122 that are not beneath theelectrode 60 generally maintain their orientation. When the long axis ofthe affected liquid crystals 120 are perpendicular to the direction ofpropagation of light 66 through the waveguide 50, or the long axis ofthe affected liquid crystals 120 are at intermediate stages such thatthey are not parallel to the propagation vector 66 (see FIGS. 6-7), thenlight 66 which is TM polarized experiences a higher index of refractionwithin the volume of liquid crystals 120 beneath the patterned electrode60. This is because the E field of the propagating light 66 interactsmore strongly with the LC molecules 120 when the LC molecules 120 areperpendicular to the direction of propagation of TM polarized light.Accordingly, as seen in FIGS. 4-7, a waveguide 50 can be formed that cancontrollably refract, steer, or focus light which is TM polarized. Inone example, the light 66 is TM polarized before it enters into thewaveguide (FIG. 7).

In FIGS. 4-7, light 66 which enters the waveguide 50 with a TEpolarization would not be affected, refracted, or steered by themovement of the affected liquid crystals 120 into the second statebecause the electric field of TE polarized light experiences the sameinteraction with the liquid crystals 120 in both the first state and thesecond state. In other words, in one example, the electric field of theTE polarized light is perpendicular to the long axis of the molecules.

With regard to FIGS. 8-11, these figures illustrate an embodiment of thepresent invention wherein the liquid crystals 58 disposed within theupper cladding 54 are aligned with their long axis perpendicular to thedirection of propagation 66 of light through the waveguide 50. Again,the alignment of the liquid crystals 58 can be biased or initiallyaligned through the use of the upper and lower alignment layers 86, 82.In this embodiment, light which is TE polarized can be refracted,steered, or focused as it travels through the waveguide 50, and further,light which is TM polarized that enters the waveguide 50 can also berefracted, steered, or focused as it travels through the waveguide 50.FIGS. 8-9 show the liquid crystals 58 in their initial, first, or zerovoltage state, where the liquid crystals 58 have been aligned with theirlong axis perpendicular to the propagation 66 of light traveling throughthe waveguide 50. For light that is TE polarized prior to entry into thewaveguide 50, the orientation of the liquid crystals 58 in the initialor first state provides a larger index of refraction than when theliquid crystals 58 are oriented vertically upward in the second state(FIGS. 10-11). Accordingly, TE polarized light can be refracted,steered, or focused through the use of this embodiment of the presentinvention. Likewise, TM polarized light can be refracted as well. For TEpolarized light, in the second state where the voltage is on, n1 isgreater than n2. For TM polarized light, in the second state wherevoltage is on, n2 is greater than n1.

While FIGS. 1-11 illustrate one example of the present invention, it isunderstood that the principles of the present invention could beemployed in other arrangements of liquid crystal waveguides, and onesuch example is illustrated in FIG. 12. In FIG. 12, an alternativeembodiment of a waveguide 130 is illustrated in accordance with thepresent invention. In this example, the ordering of the layers of thewaveguide 130 are changed when compared with FIGS. 1-2. In FIG. 12, asubstrate 132 defines the lower portion of the waveguide 130 and apatterned electrode 134 is placed on top of the substrate 132 (see alsoFIG. 13). As shown in FIG. 13, a lower cladding 136 made of non-electrooptic material may be placed on top of the electrode layer 134. The core138 layer may be placed on top of the lower cladding 136, and a loweralignment 140 layer may be placed on top of the core layer 138. An uppercladding 142 having walls 144 with liquid crystal materials 146 thereinmay be placed on top of the lower alignment layer 140, and an upperalignment layer 148 may be placed on top of the upper cladding 142. Aconductive layer or plane 150 may be placed on top of the upperalignment layer 148, and a cover plate 152 may be placed on top of theconductive layer 150. In this embodiment, the liquid crystals 146 aredisposed within the upper cladding 142. It is understood that the liquidcrystals 146 could be disposed within the lower cladding 136 if desired,and the alignment layers 140, 148 could be placed on the upper and lowersurfaces of the lower cladding 136 having the liquid crystal material146 therein.

FIG. 14 illustrates an example of operations that may be used for makingone example of a waveguide in accordance with one embodiment of thepresent invention. In making a waveguide, the materials described withreference to FIGS. 1-2 or as described otherwise herein may be used andconventional materials may be used. At operation 160 of FIG. 14, asubstrate wafer is obtained for forming the base of the waveguide. Inone example, the substrate wafer is a P-doped, polished siliconsubstrate wafer such that the substrate can act as the lower electrode,for example as in the embodiment of FIGS. 1-2. At operation 162, a lowercladding material is applied onto the substrate wafer. At operation 164,the core layer is formed on top of the lower cladding material, in oneexample. At operation 166, in one example, the wafer is diced intodesired pieces, wherein each piece will form a separate waveguide, andcleaned if desired. A conventional dicing saw for semiconductorsubstrates may be used. Cleaning may include cleaning in an ultrasoniccleaner with a mild soap or solvent, or cleaning with methanol wipes.Also, stresses from the coating process under which the waveguides aremade may induce warp and bow, which can be removed via opticallycontacting the waveguide to an optical flat or stiffener plate. Inanother example, using wafers polished on both sides and applyingthermally grown SiO2 on both sides, to a thickness of about 2 microns,can reduce the warp and bow. This thermally grown SiO2 layer may serveas the lower waveguide cladding.

At operation 168, for each piece, an alignment layer is applied adjacentto the core layer, and this combination may form a first assembly. Thereare several methods of applying the alignment layer, most of which arestandard for liquid crystal cells. These include: i) spin coat apolyimide layer, which is then buffed with a cloth (to providedirectionality); ii) buff the waveguide directly; iii) obliquedeposition of an SiO or SiO2 layer; iv) photo-align a spin-coatedpolyimide or other polymer layer via exposure to polarized light (seeFIGS. 28-32 below); v) microgrooves (see FIGS. 28-32 below); and vi)angled ion buffing.

A second assembly may be formed by operations 170, 172, 174. Atoperation 170, a piece of glass cover plate material is obtained, and atoperation 172, one or more electrodes are formed on a first side of theglass cover plate material, wherein at least one of said one or moreelectrodes has a non-normal edge or interface relative to the axis ordirection that light will propagate relative to the cover plate.Operation 172 may be implemented by applying a coating such as an indiumtin oxide (ITO) layer or any conductive layer, e.g., gold, aluminum.After this coating is applied it can be patterned via standardphoto-lithographic processes.

At operation 174, an alignment layer may be applied to the first side ofthe cover plate on top of the electrodes, thereby forming a secondassembly. This can be achieved in the same manner as operation 168. Atoperation 176 the first and second assemblies are joined together,preferably using optical glue to define a cell having three walls and anopening along the fourth wall. At operation 178, the cell is filled withliquid crystal material, and this filled structure may form the uppercladding in the example of FIGS. 1-2. Operation 178 may be implementedby establishing the cell thickness by mixing spacer balls (typically3-10 microns) into the glue that attaches the cover plate to thewaveguide. The cover plate is glued around the edges, but not in themiddle, leaving a cavity. A small hole is left in the glue seal, whichis used to fill the cavity with liquid crystal material. The cellcreated by the waveguide and cover plate is then filled with liquidcrystal. A small drop of liquid crystal material, placed at the openingor hole in the glue seal, will wick into the cell. This can be done withonly one opening or hole under vacuum, or with two holes at standard airpressure. After the cell is filled, the opening/hole in the glue seal iscovered with more glue.

It is understood that FIG. 14 is provided for illustrative purposesonly, and that these operations could be interchanged, subdivided,regrouped, or reordered depending upon the particular implementation andthe particular waveguide being made. For instance, the operations couldbe re-ordered so as to form the waveguide 130 of FIGS. 12-13, or otherwaveguide structures.

In accordance with embodiments of the present invention, a patternedelectrode 60, 134 may take various shapes depending upon the particularapplication. FIGS. 15-19 illustrate various examples of shapes forelectrodes, such as electrodes 60, 134. If it is desired to refract orsteer light over a small angle, then a simple wedge shape 180 as shownin FIG. 15 may be used for an electrode. If a larger amount ofrefraction is desired, then an electrode can include multiple wedgeshapes 182 cascaded together and electrically coupled together so thateach successive wedge 182 provides a greater amount of refraction of thelight received from the preceding wedge, as shown in FIG. 16. In FIG.17, an electrode can include a first and second electrode 184, 186wherein the first and second electrode 184, 186 are electricallyisolated. The first electrode 184 may provide a plurality of wedgeshapes 188 in series for refracting or steering light in a downwarddirection, while the second electrode 186 provides a series of cascadedwedges 190 that refracts light upwardly. Hence, the embodiment of FIG.17 can provide refraction over large angles. In use, a first voltage 192could be applied to the first electrode 184 and as the first voltage 192increases, the amount of deflection downwardly increases. As the amountof the first voltage 192 decreases, the amount of deflection decreasesuntil the point where no voltage is applied to either the first orsecond electrode and the light propagates through the waveguide in astraight line. When a second voltage 194 is applied to the secondelectrode 186 (but not the first electrode), then the light passingthrough the waveguide begins to refract upwardly as the voltage 194increases, and as the voltage 194 decreases, the amount of refractiondecreases until the point where the light passes through the waveguideis a straight line.

The angular tuning range of beamsteerer electrodes such as 184, 186shown in FIG. 17 can be limited because with successive refraction ateach prism/wedge 188, 190, the beam can be deflected sufficiently so asto exit the electrodes, and therefore no longer be steered by theremaining prisms/wedges 188, 190. In other words, the output apertureeclipses the beam, thus unnecessarily limiting the angular range. Thiscan be alleviated by: i) forming the prism array into a horn shape sothat the output aperture encompasses the full deflection range of thebeamsteerers, and ii) forming the input aperture to match to the size ofthe beam being deflected. This can increase the steering range and isgenerally discussed in: Y. Chiu, K. J. Zou, D. D. Stancil, T. E.Schelsigner, Shape-Optimized Electrooptic Beam Scanners: Analysis,Design, and Simulation, J. of Lightwave Tech., Vol. 17, p 108 (1999);and D. A. Scrymgeour, Y. Barad, V. Gopalan, K T. Gahagan, Q. Jia, T. E.Mitchell, and J. M. Robinson, Large-Angle Electro-Optic Laser Scanner onLiTaO3 Fabricated by in Situ Monitoring of Ferroelectric-DomainMicropatterning, App. Opt. Vol. 40, p. 6236 (2001), the disclosures ofwhich are incorporated by reference in their entirety. As applied toembodiments of the present invention, the outer envelope of a prismarray, which defines the maximally refracted or steered beam, may becharacterized by

$\begin{matrix}{{{\frac{\mathbb{d}^{2}x}{\mathbb{d}z^{2}} = {\frac{\Delta\; n}{n}\frac{1}{W(z)}}},{where}}{{{W(z)} = {{x(z)} + {\omega_{0\;}\{ {1 + \lbrack \frac{\lambda\; z}{\pi\; n\;\omega_{0}^{2}} \rbrack^{2}} \}}}},}} & {{Eq}.\mspace{14mu} 1}\end{matrix}$and Δn is the maximum modulation index of the waveguide, n is theaverage effective index of the guided mode, λ is the wavelength oflight, and ω is the Gaussian beam waist of the input beam. In oneexample as shown in FIG. 18, within this envelope, electrodes 200, 202can be formed with prisms 204, 206 formed by dividing the length of eachelectrode 200, 202 into N prisms 204, 206 of equal base length. Thedifferential equation describing the envelope may be solved usingnumerical methods, and an electrode pattern may be constructed. Anexample of such an electrode pattern is shown in FIG. 18, wherein afirst electrode 200 defines a plurality of successive prisms 204, and asecond electrode 202 defines a second plurality of prisms 206 opposingthe first set of prisms 204.

In a manner analogous to the two electrode beamsteerer of FIG. 17,selective application of voltage to one or the other electrode 200, 202of FIG. 18 can be used to selectively steer the beam either to one sideor the other.

Combinations of electrodes such as 180, 182, 184, 186, 200, 202 can beutilized to form optical switches wherein a first waveguide with one ormore electrodes acts as a transmitter and a second waveguide with one ormore electrodes can be positioned to receive the light transmitted bythe first waveguide.

In another example, a waveguide using the electrodes of FIG. 18 mayselectively control light (e.g. a laser beam) through an aperture, sothat a laser beam may be refracted either through the aperture orrefracted so as to not pass through the aperture, so as to be used as ashutter. This can be advantageous for construction of shutters withlight in the blue or near-UV spectral region, in part becausepolarization based shutters suffer from poor contrast ratios. In otherwords, in conventional shutters that rotate the polarization of thelight to be either blocked or not blocked by a polarizer, the off stateis typically limited by the quality of the polarizer. For example,Gallium-Nitride (GaN) diode lasers, with wavelengths around 400 nm, haveutility in optical data storage and other applications, yet high qualitypolarizers at these wavelengths are expensive, and therefore apolarization based shutter is also expensive. Using embodiments of thepresent invention, a shutter can be provided based on steering a GaNdiode beam either through or not through an aperture, and can be bothhigh contrast and inexpensive.

Furthermore, horn shaped electrodes 200, 202 can be utilized asreceiving elements. A detector element, such as a photodiode, can beplaced at the narrow end of the horn-shaped prism electrodes 200, 202(left side of FIG. 18). Depending on the amount of applied voltage toeither electrode 200, 202, the electrode pattern shown in FIG. 18 canselectively detect portions or regions of light that are entering thelarge end of the electrodes 200, 202 (the right side of FIG. 18). Inother words, for a specific applied voltage to the electrodes 200, 202,only light that enters at a specific angle and region of the electrodepattern 200, 202 (on the right side of FIG. 18) will be directed to thedetector (on the left side of FIG. 18), and therefore only that lightwill be detected. By changing the voltage applied to the electrodes 200,202, different regions and angles can be selected. In this way,electrode patterns 200, 202 such as shown in FIG. 18, can not only serveas beam steerers, but also serve as voltage controllable scanners orimagers. Combinations of these electrode patterns 200, 202 or others canserve multiple optical cross-connect and switching functions.

FIG. 19 shows an example with an electrode 210 having a parallelogramshape wherein two parallel surfaces 212, 214 are both non-normal to thepropagation direction 216 of the light input 218. In this embodiment, asthe voltage applied to electrode 216 increases, the light beam output220 passing through the waveguide can be moved to one side or another.As the voltage increases, the distance between the input beam 218 andthe active output beam 220 grows, while as the voltage decreases, thedistance between the input beam 218 and the active output beam 220decreases.

In addition to electrode shapes that can be used for beam steering asdescribed with reference to the examples above, electrode shapes mayalso be provided which focus light as it passes through the waveguide.FIG. 20 illustrates an example of operations for forming a waveguidehaving one or more electrodes with curved or lens shaped interfaces forcontrolling the propagation of light through the waveguide, inaccordance with one embodiment of the present invention. FIGS. 21-28illustrate some examples of electrodes having lens shapes that may beutilized in waveguides according to embodiments of the presentinvention.

In FIG. 20 at operation 230, a waveguide is provided with a core, uppercladding, and lower cladding, wherein liquid crystal material isdisposed within one of the claddings. As described above, the liquidcrystal material may be disposed within the upper or lower cladding, andfor purposes of this example, the liquid crystal material will bedescribed as being disposed within the upper cladding. At operation 232,one or more electrodes, also referred to herein as patterned electrodes,are provided having at least one curved or lens shaped interface or edgefor controlling the orientation of the liquid crystal material adjacent(i.e., above or below) the electrode. The curved or lens shape of theone or more electrodes induces the liquid crystal material adjacent theelectrode to form a lens shape wherein the index of refraction of thelens shape is controllable dependent upon the amount of voltage appliedto the electrode. The electrodes can be made in various such lens orcurved shapes, including conventional lens shapes, and some examples ofsuch shapes are illustrated in FIGS. 21-28. At operation 234, a lowerelectrode or plane is provided within the waveguide so that an electricfield can be formed between the one or more electrodes of operation 232and the lower electrode or plane of operation 234 in order to controlthe orientation of the liquid crystal material therebetween. In oneexample, a conductive substrate layer is provided in the waveguide toact as the lower electrode or ground plane.

At operation 236, at least one alignment layer is provided to align theliquid crystal material proximate the core. In one example, an upperalignment layer and a lower alignment layer may be provided as shown inFIG. 2 so that the liquid crystal material adjacent the alignment layeris biased or oriented in a desired orientation when no voltage isapplied between the upper patterned electrode and the lower electrode orconductive substrate; or other arrangements of alignment layers can beused. At operation 238, in one example, it is provided that light may beintroduced into the waveguide core such that the evanescent portion ofthe light wave passes through the cladding, which contains the liquidcrystal material (i.e., the upper cladding, in one example). In oneembodiment, for instance, a prism coupler or endfire coupler or otherconventional coupler may be used to introduce light into the waveguide.

At operation 240, a voltage applied between the one or more electrodesof operation 232 and the lower electrode, plane, or conductive substrateof operation 234, in order to change the index of refraction of thecladding, which contains the liquid crystal material. In operation 240,the liquid crystal material between the electrode having the curved orlens shaped interface and the lower electrode/conductive substrate iscontrollably reoriented depending upon the amount of voltage applied,and such application of voltage alters the index of refraction of suchliquid crystal material relative to light propagating through thewaveguide. As such, through the application of voltage between thepatterned electrodes and the lower electrode/conductive substrate, oneor more shapes can be formed within the liquid crystal material which ineffect operate as lenses to focus or direct light under the control ofthe applied voltage. At operation 242, the applied voltage may be variedso as to controllably focus or defocus light as it travels through thewaveguide and the evanescent portion of the light passes through theliquid crystal material experiencing the influence of the electric fieldof the applied voltage.

FIGS. 21-27 illustrate some examples of electrodes having lens shapesthat may be utilized in waveguides according to embodiments of thepresent invention. It is understood that these figures are provided asexamples only, and that the present invention contemplates any patternedelectrode forming any type of lens shape used for focusing or defocusinglight, including conventional lens shapes, or other shapes for instanceas described with reference to FIGS. 1-19. For purposes of thisdescription, it is assumed that as voltage is applied to the electrode,the index of refraction n2 of the liquid crystal material proximate theelectrode is greater than the index of refraction n1 of the liquidcrystal material outside of the electrode.

In FIG. 21, an electrode 250 is formed in the shape of a simple positivelens or plano-convex lens, wherein as the voltage applied to theelectrode 250 increases, the index of refraction n2 increases relativeto n1, and the focal length 252 is relatively short. As the voltageapplied to the electrode 250 decreases, the index of refraction n2approaches the index of refraction n1 and the focal point 254 movesoutward towards infinity. As such, the electrode 250 of FIG. 21 can beused to selectively focus light 256 along different points (e.g.,between 252 and 254) within a waveguide, and can be used forspectroscopic applications, lab on a chip, examining micro-fluidicchannels, collimation, or the like.

In FIG. 22, an electrode 260 is formed in the shape of a negative lensor plano-concave lens wherein as the voltage applied to the electrode260 increases, the index of refraction N2 increases which defocuses thelight 262. As the voltage applied to the electrode decreases, the indexof refraction N2 approaches N1, and the light rays travel substantiallyalong the same orientation as on the front side of the lens. As such,the electrode 260 of FIG. 22 can be used to selectively spread out ordiffuse light, or to collimate a converging beam of light.

Conventionally, aspherical glass lenses are difficult to make due togrinding and polishing techniques involved with making conventionalglass lenses. In contrast, aspherical curved surfaces are easilyconstructed using embodiments of the present invention. For example,embodiments of the present invention can use photolithography techniquesto form or etch one or more aspherical lens shapes in the patternedelectrode. In another example, elliptical or hyperbolic lens shapes canbe made in the patterned electrode according to the present invention,without the negative affects of spherical aberrations.

FIG. 23 illustrates an example of an electrode 270 formed in the shapeof a convex-convex lens for controlling light propagating through awaveguide, in accordance with one embodiment of the present invention.This type of lens shape may be used to focus a collimated beam of lightor to collimate a divergent beam of light. Due to the curvature of bothsides 272, 274, back reflections may be reduced. Furthermore, since bothsides 272, 274 act as focusing elements, the curvature of each side 272,274 may be reduced to achieve the same focal length as the lens of FIG.21.

FIG. 24 illustrates an example of an electrode 280 formed in the shapeof a concave-concave lens for controlling light propagating through awaveguide, in accordance with one embodiment of the present invention.This type of lens shape may be used to focus a collimated beam of lightor to collimate a divergent beam of light. Due to the curvature of bothsides 282, 284, back reflections may be reduced. Furthermore, since bothsides 282, 284 act as defocusing elements, the curvature of each side282, 284 may be reduced to achieve the same negative focal length as thelens of FIG. 22.

FIG. 25 illustrates an example of an electrode 290 formed in the shapeof a convex-concave lens for controlling light propagating through awaveguide, in accordance with one embodiment of the present invention.In this example, the radius of curvature of the front side 292 of thelens shape is greater than the radius of curvature of the back side 294.This can be useful, for instance, where it is desired to match the frontside's 292 radius of curvature with a radius of curvature of a precedinglens shape in the waveguide, or to match the back side's 294 radius ofcurvature with a radius of curvature of a subsequent lens shape in thewaveguide. As another example (not shown), Fresnel type lens patternsmay be used. Fresnel type lenses can be useful to limit the thickness ofthe lens, and such patterns can be made and applied in the presentinvention.

FIG. 26 illustrates an example of an electrode 300 formed in the shapeof a concave-concave asphere lens for controlling light propagatingthrough a waveguide, in accordance with one embodiment of the presentinvention. In this example, the radius of curvature of the front side302 of the lens shape is smaller and oppositely orientated than theradius of curvature of the back side 304. This can be useful, forinstance, where it is desired to match the front side's 302 radius ofcurvature with a radius of curvature of a preceding lens shape in thewaveguide, or to match the back side's 304 radius of curvature with aradius of curvature of a subsequent lens shape in the waveguide.Furthermore, aspherical shapes can be utilized to reduce aberrations.

In another example, two of more lens shaped electrodes may be placed inseries or cascaded or otherwise arranged to achieve various light beammanipulations, such as beam expansion, beam compression, telescoping.Since the focusing and defocusing of light through the waveguide can becontrolled electronically through the application of voltage to theelectrodes (without any mechanically moving parts), embodiments of thepresent invention can be used to replace mechanical focusing devices.For instance, a zoom function can be implemented by combining a focusingand defocusing lens in series (i.e., combining the electrode shapes ofFIG. 21 with FIG. 22; or combining the electrode shapes of FIG. 23 withFIG. 24). Further, one or more lens shaped electrodes may be placed inseries or cascaded or otherwise arranged with one or more electrodeshaving wedge/prism shapes or other non-normal interfaces such as thoseshown in FIGS. 1-2 and 15-19.

FIG. 27 illustrates another example of an electrode 310 for controllingthe propagation of light through the waveguide, in accordance with oneembodiment of the present invention. In this embodiment, the electrode310 includes an opening or hole region 312 that defines at least onenon-normal interface or curved or lens shaped edge 314 relative to thedirection 316 of propagation of light 318 traveling through thewaveguide. While in this example the opening 312 defines a singlewedge/prism shape, it is understood that other shapes could be used aswell, such as shapes having non-normal interfaces or curves or lensshapes, for instance, as shown in FIGS. 15-19 or 21-26, and that theelectrode may include multiple openings in series or cascaded. In thiscase, when no voltage is applied to electrode 310, the index ofrefraction n2 of the region adjacent the opening 312 is approximatelyequal to the index of refraction of the region adjacent the electrode;and as voltage is applied to the electrode 310, the index of refractionn1 of the region adjacent or proximate the electrode 310 changes.

FIG. 28 illustrates an alternative embodiment wherein a waveguide 320utilizes an alignment layer 322 having two or more areas or regions 324,326 having different orientations that align the liquid crystal material328 in the adjacent cladding 330 so as to form refractive shapes 332within the liquid crystal material 328 for controlling light propagatingthrough a waveguide 320, in accordance with one embodiment of thepresent invention. In one example and referring to FIGS. 28-30, thewaveguide 320 can be constructed in a manner similar to the embodimentsdescribed above except that in place of one or more patternedelectrodes, the embodiments of FIGS. 28-30 have an alignment layer 322with regions 324, 326 of patterned alignments and a pair of electrodelayers 334, 336 or planes. Hence, the waveguide 320 of the example ofFIG. 28-30 may include a substrate 338 acting as a lower electrode plane336, a lower cladding 340, a core layer 342, an alignment layer 322having the one or more regions 324, 326 defining various shapes, anupper cladding 330 with liquid crystal material 328 therein, an upperelectrode plane 334, and a glass cover 344. The substrate 338, lowercladding 340, core 342, upper cladding 330 with liquid crystal material328 therein, and the glass cover 344 can all be made as described abovewith reference to FIGS. 1-14. The upper electrode 334 can be implementedas a conductive coating or conductive layer as described above withreference to FIGS. 1-14.

On the alignment layer 322, the one or more areas or regions 324, 326can define various shapes 332 in order to induce the liquid crystalmaterial 328 in the adjacent upper cladding 330 to form various shapeswhen no voltage 346 is applied, such as shapes 332 having non-normalinterfaces (such as one or more of the shapes shown in FIGS. 1-2 and15-19 or shapes having curves or lens shapes such as one or more of theshapes shown in FIGS. 21-26).

In the example of FIG. 28, the alignment layer 322 of the waveguideincludes a first region 324 and a second region 326. In this example,the second region 326 aligns the liquid crystal materials 328 in theupper cladding with their long axis perpendicularly orientated relativeto the propagation direction 348 of light 350 traveling through thewaveguide 320; and the first region 324 defines a wedge or prism shape332, wherein within the first region 324, the liquid crystal materials328 in the upper cladding 330 are aligned with their long axisorientated in parallel relative to the propagation direction 348 oflight 350 traveling through the waveguide 320 (see FIGS. 29, 31).

In operation, when no voltage 346 is applied between the upper electrode334 and the lower electrode/substrate 336, the index of refraction n1 ofthe second region 326 is greater than the index of refraction n2 of thefirst region 324 for TE polarized light traveling through the waveguide320 (see FIGS. 29, 31). As a voltage 346 is applied between the upperelectrode 334 and the lower electrode/substrate 336, the electric fieldof the applied voltage 346 induces the liquid crystals 320 within theupper cladding 330 to orient vertically (see FIGS. 30, 32), andtherefore for TE polarized light traveling through the waveguide 320,the index of refraction n1 of the second region 326 is approximatelyequal to the index of refraction n2 of the first region 324, and norefraction or light bending occurs.

As with the other embodiments disclosed herein that use patternedelectrodes to induce portions of the liquid crystal materials to formvarious refractive or lens shapes, the embodiments of FIGS. 28-32 can bemade using different arrangements, liquid crystal alignments, or ordersof layers as desired.

FIG. 33 illustrates an example of operations for forming a waveguidehaving an alignment layer with two or more areas or regions havingdifferent orientations that induce or align the liquid crystal materialin the adjacent cladding to form refractive shapes within the liquidcrystal material for controlling light propagating through a waveguide,in accordance with one embodiment of the present invention. The shapesof the regions can include shapes with non-normal interfaces, or curvedor lens shaped interfaces.

In FIG. 33 at operation 360, a waveguide is provided with a core, uppercladding, and lower cladding, wherein liquid crystal material isdisposed within one of the claddings. As described above, the liquidcrystal material may be disposed within the upper or lower cladding, andfor purposes of this example, the liquid crystal material will bedescribed as being disposed within the upper cladding. At operation 362,an upper electrode or plane is provided, and at operation 364, a lowerelectrode or plane is provided within the waveguide. In one example, theupper electrode is formed as a conductive coating on the glass cover oras a layer of conductive material. In one example, a conductivesubstrate layer or other conductive layer is provided in the waveguideto act as the lower electrode or ground plane.

At operation 366, at least one alignment layer is provided to align theliquid crystal material in the upper cladding proximate the core. In oneexample, the alignment layer has two or more regions with differingalignments so that the liquid crystal material adjacent the alignmentlayer is biased or oriented in a desired orientation when no voltage isapplied between the upper electrode and the lower electrode. The shapesof the regions can include, for instance, shapes with non-normalinterfaces, refractive shapes, prisms, wedges, curved or lens shapessuch as those described above.

As with the above described embodiments, the non-normal interfaces,refractive shapes, curved or lens shapes of regions of the alignmentlayer induce the liquid crystal material in the adjacent cladding toform a corresponding shape wherein the index of refraction of the formedshape is controllably dependent upon the amount of voltage applied tothe electrodes.

As to operation 366, one example of how a region or area of thealignment layer can be patterned or made is by utilizing regions ofphoto-aligned polyimide, such as by companies such as Elsicon Inc., orother photo-aligned polymers or other general photoalignable materials.Liquid crystal molecules in the adjacent cladding will generally alignaccording to the orientation of these regions of polymer.

Specifically, the polymer may be spin-coated directly onto the surfaceof the waveguide core, and such application may occur in the same manneras how normal polymer would be applied to the core. Polarizedultraviolet light may be applied to selected regions of the polymer tocreate alignments within such regions. The direction of polarization ofthe ultraviolet light determines the director, or liquid crystalorientation or direction, i.e., the alignment.

In order to create regions of patterned alignment, a first mask can becreated which would be placed directly above the polymer to cover thepolymer during exposure to ultraviolet light. Patterns of opaque regionson the mask would cast shadows onto the polymer, and therefore thesedark regions would not be aligned. The ultraviolet light source wouldthen be turned off and the mask removed.

A second mask that is a negative or inverse of the first mask could thenbe placed directly above the polymer to cover the polymer during asecond exposure to ultraviolet light. For the second exposure, thedirection of polarization of the ultraviolet light, with respect to thewaveguide, is then rotated ninety degrees. When the ultraviolet light isturned on during the second exposure, the regions that were previouslynot exposed (and therefore not aligned) are now aligned. Since thedirection of polarization of the ultraviolet light (with respect to thewaveguide) has been rotated ninety degrees, the alignment in theseregions will be rotated ninety degrees with respect to the alignmentoutside of these regions. Using this method, various regions on thealignment layer can be formed having different alignments so that thepolymer induces the liquid crystal material in the adjacent cladding toalign according to the polymer patterns of the alignment layer.

Alternatively, in another example, a polymer can be applied anduniformly buffed. A photoresist can then be applied and exposed in thedesired pattern. The photoresist is then removed in the area of thepattern and the polyimide is buffed in a different or orthogonaldirection. The remaining photoresist is then removed.

Another example of operation 366 to form a patterned or aligned regionor area is via etching microgrooves directly into the top of thewaveguide core. The width and distance between adjacent microgrooves ischosen to be sufficiently small so that it does not effect thepropagation of the light in the core. Liquid crystal molecules in theadjacent cladding will generally align according to the orientation ofthese microgrooves.

To create microgrooves, in one example photo-resist may be applied tothe core and then cured using an interference pattern between twoshort-wavelength beams. This creates a pattern of closely spaced linesof photo-resist on the core. Standard etching techniques are then usedto remove a small amount of the core in the regions that are not coveredby the lines of photo-resist. The photo-resist is removed, and amicrogrooved pattern is left on the core.

Two or more regions of microgrooves can be formed on the alignment layer(or on the surface of the core), wherein each region has a set ofaligned microgrooves, and the alignment of a first region differs fromthe alignment of a second region. This can be done by maskingtechniques. Specifically, a patterned mask can be inserted prior toexposing the photo-resist to the short wavelength interference pattern.The photoresist will not be cured in the regions that are shadowed bythe mask. The short wavelength light is turned off and the mask isremoved. A negative of the first mask is then inserted. The interferencepattern created by the short wavelength light is then rotated ninetydegrees with respect to the waveguide. The short wavelength light isthen turned on, and the exposed regions of the photo-resist are cured inclosely spaced lines, but these lines are now rotated ninety degreeswith respect to the previously cured lines. The waveguide is then etchedusing standard techniques. The net result is two regions, both withmicrogrooves, but the directions of the microgrooves in one region isrotated ninety degrees with respect to the direction of the microgroovesin the other region. Using this technique, various regions on thealignment layer can be formed having different alignments so that themicrogrooves induce the liquid crystal material in the adjacent claddingto align according to the regions of microgroove patterns of thealignment layer.

As another example, nano-imprint lithography techniques can be used tocreate regions of patterned alignment. In this technique, a pattern,such as the microgroove pattern described above, can be used to imprintthe pattern onto a softer substrate.

At operation 368, in one example, it is provided that light may beintroduced into the waveguide core such that the evanescent portion ofthe light wave passes through the cladding, which contains the liquidcrystal material (e.g., the upper cladding, in one example). In oneembodiment, for instance, a prism coupler or butt-coupling or end-firecoupling technique or other conventional method or device may be used tointroduce light into the waveguide.

At operation 370, a voltage is applied between the upper and lowerelectrodes of operations 362-364 in order to change the index ofrefraction of the upper cladding, which in this example contains theliquid crystal material. As voltage is applied between the upper andlower electrodes, an electric field is formed between the upper andlower electrodes in order to control the orientation of the liquidcrystal material therebetween.

In operation 370, the liquid crystal material between the upperelectrode and the lower electrode is controllably reoriented dependingupon the amount of voltage applied, and such application of voltagealters the index of refraction of such liquid crystal material relativeto light propagating through the waveguide. As such, through theapplication of voltage between the upper and lower electrodes, one ormore shapes can be formed within the liquid crystal material which ineffect operate as prisms, refractive elements, or lenses to bend, focus,defocus, or direct light under the control of the applied voltage. Atoperation 372, the applied voltage may be varied so as to controllablyrefract/bend, focus or defocus light as it travels through the waveguideand the evanescent portion of the light passes through the liquidcrystal material experiencing the influence of the electric field of theapplied voltage.

FIG. 34 illustrates an alternative embodiment wherein a waveguide 380utilizes a cladding 382 that includes at least two regions 384, 386: aregion 384 without liquid crystal material 388 and a region 386 withliquid crystal material 388. In one example, the first region 384 mayinclude a non-liquid crystal material, such as but not limited to any ofthe materials that can be used to create the lower cladding as discussedpreviously with respect to FIGS. 1-14. In one example, this first region384 is generally not electro-optic, i.e., the index of refraction doesnot change with respect to an applied electric field. The second region386 may comprise areas or refractive shapes or cavities 390 where thenon-liquid crystal material of the first region is not present or isreduced in thickness so as to create cavities or chambers 390 into whichliquid crystal material 388 is placed and the evanescent wave of theguided light 389 will penetrate. In this manner, dynamically voltagetunable refractive shapes 392 are constructed by controlling the shapeor area 390 in which the liquid crystal 388 may interact with the guidedlight 389 via the evanescent wave. Of course, the cladding 382 with thecavity 390 with liquid crystal material 388 therein could be the uppercladding 382 or the lower cladding 394, depending on the implementation.

In one example and referring to FIGS. 34-36, a waveguide 380 can beconstructed in a manner similar to the embodiments described aboveexcept that in place of one or more patterned electrodes, theembodiments of FIGS. 34-36 have an upper cladding 382 in which onlyregions or areas 386 contain liquid crystal material. Hence, thewaveguide 380 of the example of FIG. 34-36 may include a substrate 396acting as a lower electrode plane, a lower cladding 394, a core layer398, an alignment layer 400, an upper cladding 382 with a region or area386 with liquid crystal material 388 therein and a region 384 withnon-liquid crystal material therein, and an upper electrode plane 402. Asecond alignment layer 404 may be provided between the upper electrode402 and the upper cladding 382, if desired. A glass cover 406 may alsobe used if desired. The substrate 396, lower cladding 394, core 398,upper cladding region 386 with liquid crystal material 388 therein, andthe glass cover 406 can all be made as described above with reference toFIGS. 1-14. The upper electrode or plane 402 can be implemented as aconductive coating or conductive layer as described above with referenceto FIGS. 1-14.

On the upper cladding 382, the one or more areas or regions 386 in whichliquid crystal material 388 interacts with the guided light 389 candefine various shapes 392, such as refractive shapes having non-normalinterfaces (such as one or more of the shapes shown in FIGS. 1-2 and15-19 or shapes having curves or lens shapes such as one or more of theshapes shown in FIGS. 21-26).

In the example of FIG. 34, the second region 386 may comprise a wedgeshape where the non-electro optic material of the upper cladding 382 isabsent and the core layer 398 is therefore exposed. In this second area386, an alignment layer 400 and liquid crystal material 388 are disposedtherein and may operate in a fashion analogous to that previouslydiscussed in reference to FIGS. 1-15. In this particular example, thelong axes of the liquid crystal molecules 388 in the second region 386are aligned so that at low or zero voltage 408 their alignment directionis predominantly parallel to the direction 410 of light 389 propagatingthrough the waveguide 380 (see FIG. 35), although other orientations arepossible.

In operation and referring to FIGS. 34-38, when no voltage 408 isapplied between the upper electrode 402 and the lowerelectrode/substrate 396, the index of refraction n1 of the first region384 is different than the index of refraction n2 of the second region386 for TM polarized light traveling through the waveguide (see FIGS.35, 37). As a voltage 408 is applied between the upper electrode 402 andthe lower electrode/substrate 396, the electric field of the appliedvoltage 408 induces the liquid crystals 388 within the second region 386of the upper cladding 382 to orient vertically (see FIGS. 36, 38), andtherefore for TM polarized light traveling through the waveguide 380,the difference between the index of refraction n1 of the first region384 and the index of refraction n2 of the second region 386 is changed.Depending on the index of refraction of the first region 384 (which inthis example is constant and not voltage tunable, but can be chosen froma range of values), the degree or amount of refraction of the waveguide380 will change. In other words, since the difference between n1 and n2can be voltage tuned, the degree of refraction can also therefore bevoltage tuned. However, unlike the embodiments using shaped electrodes,the refraction at zero voltage will not generally be zero, unless thefixed index of region 384 is deliberately chosen to equal the index ofthe liquid crystal 388 at zero volts.

As with the other embodiments disclosed herein that use patternedelectrodes to induce portions of the liquid crystal materials to formvarious refractive or lens shapes, the embodiments of FIGS. 34-38 can bemade using different arrangements of layers, different liquid crystalalignments, or different orders of layers as desired. Depending on theimplementation, refraction of TE or TM polarized light (or both) can beachieved.

FIG. 39 illustrates an example of operations for forming a waveguidehaving a cladding layer with two or more areas or regions, the firstregion having non-liquid crystal material and the second region havingliquid crystal material to form refractive shapes within the claddingfor controlling light propagating through a waveguide, in accordancewith one embodiment of the present invention. The shapes of the regionscan include refractive shapes with non-normal interfaces, for examplewedge or prism shapes or curved or lens shaped interfaces. In theexample of FIG. 39, a cavity or region with liquid crystal material isprovided in the upper cladding, although it could be provided in thelower cladding.

In FIG. 39 at operation 420, a waveguide is provided with a core, anupper cladding, and a lower cladding.

At operation 422, in one example, regions or areas of the upper claddingare removed thereby forming shapes or areas in which the core layer maybe exposed. This may be achieved with standard photolithographictechniques. For example, a photomask may be used to cure a patternedphotoresist on top of the upper cladding layer. Etching techniques arethen used to remove portions of the upper cladding in regions where thephotoresist has not been cured. The upper cladding may be etched with achemical process that only removes the upper cladding material and notthe core, which will prevent the core from being etched into or etchedthrough (etching through the core would destroy the waveguide).Alternatively, the upper cladding can be etched for a sufficient time tosignificantly reduce the thickness of that region of upper cladding, butnot completely remove the non-liquid crystal cladding. Such a techniquecan create regions into which the evanescent wave will penetrate. Asanother alternative, a chemical stop layer may be applied between thecore and upper cladding layer. This chemical stop layer will preventetching into the core, and can be made sufficiently thin so as to notadversely affect the optical properties of the waveguide. Finally, theetched cavity region can be constructed so as to provide an opening atthe edge of the waveguide. This can facilitate filling the chamber orcavity of the cladding with liquid crystal material.

At operation 424, an alignment layer is provided for biasing the liquidcrystal material that will be disposed within the etched cavity regionsof the upper cladding. This can be accomplished by the alignmenttechniques previously mentioned. However, since the upper surface is nolonger of uniform height (regions have been etched away), application ofan alignment layer can become more challenging. For example, spincoating techniques (for application of a polyimide or polymer layer)will tend to planarize the surface and therefore be undesirably thick inthe etched regions. One technique to avoid this problem is to create theetched regions or cavities such that they extend to the edge of thewaveguide. The waveguide can then be placed on a spin coater off-center,and oriented so that excess material will have a path to be removed viacentrifugal forces of the spin coat process. Alternatively, obliquedeposition of SiO and/or SiO2 can provide an alignment layer, with onlyminimal shadows created by the edges of the etched regions. As anotheralternative, prior to applying the non-liquid crystal upper claddingmaterial, a microgroove alignment layer may be created along the entirewaveguide core via holographic lithography or nano-imprint techniques.The non-liquid crystal upper cladding would then be applied, and afteretching away regions or cavity areas to expose the core, the alignmentlayer would already be present there.

At operation 426, an upper electrode or plane is provided. This upperelectrode or plane may also form the ceiling of the chamber or cavity tobe filled with liquid crystal. In one example, the upper electrode isformed as a conductive coating on the glass cover or as a layer ofconductive material.

At operation 428, the chamber or cavity in the upper cladding may befilled with liquid crystal material. With only one opening, as depictedin the example of FIG. 34, this process may be conducted under a vacuum.A drop of liquid crystal material placed adjacent to the opening willwick into the chamber or cavity. This chamber may be plugged with astandard glue after filling.

At operation 430, a lower electrode or plane is provided. In oneexample, a conductive substrate layer or other conductive layer isprovided in the waveguide to act as the lower electrode or ground plane.

At operation 432, in one example, light may be introduced into thewaveguide core such that the evanescent portion of the light wave passesthrough the cladding that contains both the regions with and without theliquid crystal material (e.g., the upper cladding, in one example). Inone embodiment, for instance, a prism coupler or butt-coupling orendfire coupling technique or other conventional method or device may beused to introduce light into the waveguide.

At operation 434, a voltage is applied between the upper and lowerelectrodes of operations 426-430 in order to change the index ofrefraction of the sections or cavity areas of the upper cladding whichcontain the liquid crystal material. As voltage is applied between theupper and lower electrodes, an electric field is formed between theupper and lower electrodes in order to control the orientation of theliquid crystal material therebetween.

In operation 436, the liquid crystal material in the shaped cavitiesbetween the upper electrode and the lower electrode is controllablyreoriented depending upon the amount of voltage applied, and suchapplication of voltage alters the index of refraction of such refractiveshapes of liquid crystal material relative to light propagating throughthe waveguide. Such shapes that contain the liquid crystal material ineffect operate as prisms, refractive elements, or lenses to bend, focus,defocus, or direct light under the control of the applied voltage. Atoperation 436, the applied voltage may be varied so as to controllablyrefract/bend, focus or defocus light as it travels through the waveguideand the evanescent portion of the light passes through the liquidcrystal material experiencing the influence of the electric field of theapplied voltage.

As explained above, embodiments of the present invention may be used invarious applications. FIGS. 40-42 illustrate two examples of suchapplications. In FIG. 40, a barcode scanner or laser print head 440 isformed utilizing a waveguide 442 having a lens shaped electrode 444 anda plurality of prism shaped electrodes 446. In this example, a laserlight source 448 passes a laser beam 450 through a lens 452, whichdirects the laser beam 450 into the waveguide 442, and within thewaveguide 442, depending upon the voltages 455 applied to the patternedelectrodes 444, 446 therein, the angle at which the light beam 450 exitsthe waveguide 442 is controlled. Hence, the output beam 454 of light canbe dynamically steered to scan or read a barcode 456, and the reflectedlight can be read by optical receiving devices such as photodiodes (notshown). In this example, the optical portion 458 of the barcode scanner440 does not use any moving parts. Instead, the direction of the outputlight beam 454 is controlled by the voltages 455 applied to thepatterned electrodes 444, 446.

FIG. 41 illustrates another example of an electrode for controlling thepropagation of light through a waveguide, in accordance with oneembodiment of the present invention. In this embodiment, the electrode460 includes multiple slits, gaps, or slots, 462 in the electrode 460.In one example, the electrode 460 includes multiple fingers orrectangles 464, or a comb structure, where each rectangle 464 isseparated from the adjacent rectangle by a small space or slit 462. Therectangles 464 are electrically connected along one end 466; forexample, in FIG. 41 the rectangles 464 are connected along the bottomedge 468 of the electrode 460. Furthermore, multiple points 470, 472,474 are provided for connection of multiple voltages 476, 478, 480 tothis electrode 460. If the voltages 476-480 applied to all of theconnection points 470-474 are the same, then this electrode 460 acts asa uniform plane, which can be used to change the index of refraction ofliquid crystal material under, proximate, or otherwise adjacent to thiselectrode 460. Alternatively, the voltages 476-480 applied to thedifferent connection points 470-474 may be chosen to be different fromone another. In this case, a voltage gradient will exist from oneelectrode connection point 470, 472, or 474 to another. The magnitude ofthis voltage gradient will be dependent on the magnitude of thedifferences in the voltages 476-480 applied to the different connectionpoints 470-474. The electrode 460 can be designed to have a sufficientlyhigh resistance, such that a voltage gradient or difference can bemaintained with only limited current flowing through the electrode 460.This voltage gradient, which exists between the connection points470-472-474, will be extended, via the rectangular shapes 464, to covera region of a waveguide over which this electrode pattern extends. Inthis way, a gradient in the index of refraction of a waveguide can becreated and dynamically controlled, by controlling the differentvoltages 476-480 at the different connection points 470-474. AlthoughFIG. 41 shows an electrode 460 with three connection points 470-474, itis understood that any number of connection points can be utilized.

A waveguide may be formed utilizing any of the structures previouslydiscussed, wherein an out-coupling grating is included in the waveguide.Out-coupling gratings can be constructed by deliberately creating aperiodic variation in the index of refraction within a waveguide. Thismay be done, for example, by providing a core layer with periodicvariations in its thickness, as is shown in FIGS. 42-44. Alternatively,either the core or one of the claddings may be constructed so as to havea periodically varying index of refraction (e.g., the core layer may bedoped with materials having different indexes of refraction. The spacingor pitch between index variations may be chosen so that light will bedirected out of the waveguide. In one example, the angle at which thelight is out-coupled, (e.g., the angle of propagation of the light thatleaves the waveguide) is dependent in part on the pitch or spacing ofthe out-coupling grating. As recognized by the present inventors, bydynamically changing this pitch, a waveguide can be formed so that theangle at which the light leaves the waveguide can be dynamicallychanged.

In one example, an out-coupling grating can be combined with a patternedelectrode of FIG. 41 to control the angle at which light leaves awaveguide. For example, in FIGS. 42-44, a waveguide 500 may include anout-coupling grating 501 formed by a core 502 having a periodicallyvarying thickness. A cladding 504 having liquid crystal material and anelectrode 508 with slots 510 (e.g., FIG. 41) may be placed on top of thecladding 504. A lower substrate 512 provides both structural support forthe waveguide 500 and the electrical ground for all voltages appliedbetween the connection points and the substrate 512. The sub-cladding514 (e.g., lower cladding), core 502, liquid crystal upper cladding 504,and alignment layers 516 can be constructed as discussed previously.

In order to construct an out-coupling grating 501, in one example apattern of grooves 520 can be created in the lower cladding 514 prior toapplication or formation of the core layer 502. This groove pattern 520may be constructed with photo-lithographic techniques. After the corelayer 502 is applied, a chemical-mechanical polishing step can be usedto smooth out the top surface of the core layer 502. Also, the depth andspacing of the out-coupling grating can be tapered from one side (e.g.,entrance) to the other (e.g., distal) of the waveguide 500. Suchtapering techniques can be utilized to alter or condition the shape ofthe out-coupled light beam.

Light 522 is input into the waveguide 500, and the light output 524leaves the waveguide 500 due to the out-coupling grating 501. The angleat which output light 524 leaves the waveguide 500 depends in part onthe voltages 530-534 V3, V4, V5 applied to the electrode 508.

As with FIG. 41, the electrode 508 of FIGS. 42-44 may have variouspoints at which different voltages may be applied. In the example shownin FIG. 41, three voltages (530, 532, 534) are represented as V3, V4,and V5.

It is understood depending upon the implementation, a waveguide can beformed with an out-coupling grating 501 or variation thereof incombination with one or more different electrodes, including but notlimited to a comb-type electrode (such as 460 or 508), a prism or wedgeshape electrode, a lens shaped electrode, or an electrode which has aplane or shape. Conversely, an electrode such as electrode 460 can beused in a waveguide that has a core layer as described with reference toFIGS. 1-30 or a waveguide or core layer having an out-coupling gratingsuch as grating 501 of FIGS. 42-44.

Referring to FIG. 42, if no voltage is applied to the patternedelectrode 508 (e.g., V3=V4=V5=0), then the index of refraction for theliquid crystal material 506 underneath the electrode 508 will beuniform. The out-coupling grating 501 formed by the core 502 will thendirect the light 524 out of the waveguide 500 at an angle that isdetermined by the pitch of the out-coupling grating 501. As shown inFIG. 42, this angle will be constant along the length of the grating501. When light 522 first enters the core 502 with out-coupling region501, it will begin to leave the waveguide 500 at an angle that isdetermined by the pitch of the grating 501. As the light 522 propagatesalong the length of the out-coupling grating 501, the light beam 524will exit the waveguide 500 until all of the light 524 has beenout-coupled or the out-coupling grating 501 ends.

Shown in FIG. 43 is the case where a high-voltage has been applied toall of the connection points (e.g., V3, V4, V5) of electrode 500. Inthis case, the index of retraction of the liquid crystal material 506 incladding 504 will be uniform, but different than the index of refractionthat corresponds to zero voltage in FIG. 42. The change in the index ofrefraction of the upper cladding 504 will alter the index of refractionfor the guided light, as has been discussed previously, and changes inthe effective pitch of the out-coupling grating 501. Since this pitch iseffectively different, the angle at which light 524 exits or isout-coupled from the waveguide 500 will therefore also be different. Inthis way the angle at which light 524 exits the waveguide 500 may becontrolled by controlling the voltage V3, V4, V5 applied to thepatterned electrode 508. In the example of FIGS. 42-43, the light 522 isassumed to be TM polarized, in which case higher voltage will direct thelight 524 out of the waveguide 500 at a steeper angle relative to thewaveguide normal. For lower voltage and TM polarized light, the outputangle of light 524 with respect to the waveguide normal will be smaller.In this way, one may dynamically control the angle of light 524 leavingthe waveguide 500 by controlling the magnitude of applied voltage (e.g.,V3, V4, V5).

Shown in FIG. 44 is the case where the voltages (e.g., V3, V4, V5)applied to different connection points of electrode 500 are not thesame. Specifically, shown in FIG. 44 is the case where the voltage V3 iszero, the voltage V4 is intermediate, and the voltage V5 is higher thanV4. In this case, the index of refraction of the liquid crystal material506 underneath the electrode 508 is varying. This varying index ofrefraction will result in a varying out-coupling angle of light 524, asis shown in FIG. 44 for TM polarized light 522. By controlling themagnitude of the differences between the voltages V3, V4, V5, the angleat which the light 524 leaves the waveguide 500 can be controlled aswell as the focusing of the out-coupled light 524. Shown in FIG. 44 isan example where the voltage differences between V3, V4, V5 are chosenso that the out-coupled light 524 is coming to a focus. Therefore, notonly can the angle of the out-coupled light 524 be dynamicallycontrolled with the voltages (e.g., V3, V4, V5), but also the focusingproperties of the light 524.

In FIGS. 45-46, an optical read/write head 550 for a CD/DVD playerincludes a waveguide 552 having a plurality of patterned electrodes 554,556, 558 for controlling light, in accordance with an embodiment of thepresent invention. FIGS. 45-46 are an adaptation of a figure in S. Ura,T. Suhara, H. Nishihara, and J. Koyama, An Integrated-Optic Disk PickupDevice, IEEE J. Lightwave Technology, LT-4, Vol. 7, pages 913-918,(1986), the disclosure of which is incorporated by reference in itsentirety. In the example of FIGS. 45-46, the device 550 is dynamic dueto the liquid crystal waveguide 550 and its electrode elements 554-558.In this example, three patterned electrodes 554, 556, 558 are providedfor dynamic steering and focusing. Application of voltages V1 and V2steers and focuses the beam 560 in the dimension of the waveguide plane.The electrodes 554, 556 are a focusing or lens shape (554) and asteering or prism shape (556). The voltages V3, V4, and V5 are appliedto a patterned electrode 558, similar to as shown in FIG. 41. In FIGS.45-46, this electrode 558 is placed above an out-coupling grating (562).As discussed above, the ratios and magnitude of voltages V3, V4, and V5,give both steering and focusing of light 564 out of the waveguide 552.In this example, the out-coupling grating 562 also serves as anin-coupling grating. Light that is directed out of the waveguide willhit an optical storage medium (such as a compact disc), and the lightthat is reflected off of that medium will be re-coupled back into thewaveguide. This is the return beam. Shown in FIGS. 45-46 is anintegrated optical lens 566, which serves to both collimate the lightfrom the laser diode 568 and also to focus the return light ontodetection photodiodes 570. The detection photodiodes 570 are actuallyphotodiode pairs. Shown in FIG. 46 is a beamsplitting grating 572, whichsplits the return beam into two parts that focus the returned light ontothe photodiodes 570. If the surface of the optical storage medium is tooclose, the beams fall towards the outer photodiodes of pairs 570. Atracking error 574 shifts intensity between the upper and lowerphotodiode pairs 570. The circuitry 576 of FIG. 46 shows an example ofhow the focusing, tracking, and signal from the CD or other opticalstorage media can be amplified and measured.

Electrode Example One

Described below is one example of a liquid crystal waveguide in whichthe waveguide provides for an increased modulation index, and this isdescribed as an example only. It is understood that this example isprovided for illustrative purposes only, and does not limit the scope ofembodiments of the present invention. In this example, a waveguidedevice may be formed utilizing a heavily p-doped silicon wafer, withboth sides polished, as the lower electrode. Upon the p-doped siliconwafer, a thermally oxidized lower cladding can be grown with a thicknessof 2±0.05 microns. The lower cladding refractive index at a wavelengthof 1550 nanometers was 1.445±0.001 as measured by a broadbandellipsometer. A SiOxNy guide layer or core was applied over the lowercladding by plasma enhanced chemical vapor deposition to a thickness of800.3±7 nanometers. The ratio of Ox to Ny in SiOxNy was adjusted duringthe deposition process to create a core with a refractive index of1.811±0.005 at a wavelength of 633 nanometers and a refractive index of1.793±0.005 at a wavelength of 1550 nanometers. Identical coatings wereapplied to both sides of the wafer in order to balance stresses, andtherefore mitigate warping or bending of the wafer. These stresses are aresult of the plasma enhanced chemical vapor deposition process. Arectangle/parallelogram was created as the upper electrode usingstandard photolithographic techniques, specifically, standard maskingand chemical etching pattern the ITO on the glass cover plate.

Once complete, the wafer was diced into smaller 10 millimeter by 25millimeter parts. Each diced part was then coated with an alignment filmapproximately 120 angstroms in thickness. The alignment film was used tocreate the homeotropic orientation of the liquid crystal upper cladding.The film was produced by spin coating an 8:1 mixture of Nissan polyimidevarnish solvent #26 to Nissan polyimide type 1211 filtered at 0.2microns at 2500 rpm. The same spin coating process was performed on thecover plate, which was made of 0.7 millimeter thick 1737 corning floatglass coated on one side with an indium tin oxide (ITO) film to producethe 100 ohms/square conductive layer used for the upper electrode.

Once both the wafer and the cover glass were coated, the polyimide wasimidized by baking in an oven at 200 degrees celcius for approximately 1hour. The polyimide coatings were mechanically buffed with a dense piledcloth to induce preferential alignment along the light wave propagationdirection of the waveguide. The liquid crystal upper cladding layer wasformed by spacing the ground plane 1737 glass window from the dicedwafer parts with 5-micron borosilicate glass spacers immersed in anultra-violet curing adhesive Norland 68. Approximately 1-millimeter dotsof the spacing mixture were placed at the four corners that created thecell gap for the liquid crystal to be disposed therein. The cover platewas attached to the rest of the waveguide so as to create ananti-parallel alignment layer on the waveguide core. The cell gap wasthen exposed to 365 nanometer light until fully cured. Straight Norland68 was used to backfill via capillary action the remaining exposed edgesmaking up the cell gap. Two 1-millimeter openings were left, one on eachopposite side on the edges 90 degrees to the buff direction. MBBA liquidcrystal, obtained from Aldrich Chemical Co., was then introduced to oneof the two edge openings and allowed to fill the cell gap via capillaryforce. Once filled, the holes were plugged by using Norland UVS-91visible-uv curing adhesive. Wires were then attached to the upperelectrode and lower electrode using conductive epoxy.

In this example, operation of the waveguide included coupling light intoand out of the waveguide by means of gadolinium gallium garnet GGG30-60-90 prisms. Equal amounts of TE and TM light were introduced intothe TE0 and TM0 modes of the waveguide. Amplitude modulated 15 KHzsquare-wave drive voltages were applied to change the TM phaserelationship to TE. To measure this change in phase relationship, a45-degree polarizer prism was used to interfere the TE and TM light.

Table 1 shows hypothetical calculations of Beam Deflection (in degrees)as a function of applied voltage. The modulation index, which is thedifference between n2 and n1, is experimental data as different voltagesare applied to a waveguide made according to this example, with awavelength of light of 1320 nm. Using this experimental modulation indexdata, a theoretical beam deflection can be calculated using Snell's lawwith the assumption that light is passed through a prism or wedge ortriangular shaped electrode having a right angle and a small angle of8.44 degrees.

TABLE I Theoretical Beam Deflection Theoretical Volts Modulation BeamDeflection (RMS) Index Change (Δn) (degrees) 3.7 0.00015 −0.01521 7.90.001353 0.248549 9.7 0.001954 0.38367 12.2 0.002706 0.555834 140.003308 0.696327 15.9 0.003909 0.839424 17.8 0.00451 0.985276 19.50.004961 1.096573 22.7 0.005713 1.28593 26 0.006615 1.520026 28.50.007216 1.680617 32 0.007968 1.886918 37.4 0.009321 2.275752 45.70.010374 2.596174 50 0.010825 2.739055 59.3 0.011877 3.087396 72.50.01308 3.515909 90 0.014282 3.985982 92.5 0.014433 4.048325 1100.015335 4.443064 125 0.015936 4.729873 129 0.016086 4.805172 1600.016989 5.295375 181 0.01744 5.572446 212.5 0.018041 5.991477 2460.018492 6.362253 326 0.019244 7.220316 358 0.019394 7.48663

Electrode Example Two

Described below is one example of a liquid crystal waveguide in whichthe waveguide was designed to provide for approximately 28.7 degrees inbeam steering, and this is described as an example only. It isunderstood that this example is provided for illustrative purposes only,and does not limit the scope of embodiments of the present invention. Inone example, a waveguide beam steering device may be formed utilizing aheavily p-doped silicon wafer, with both sides polished, as the lowerelectrode. Upon the p-doped silicon wafer, a thermally oxidized lowercladding can be grown with a thickness of 2.16±0.05 microns. The lowercladding refractive index at a wavelength of 633 nanometers was1.458±0.001 as measured by a broadband ellipsometer. A stoichiometericSi3N4 guide layer or core was applied over the lower cladding bylow-pressure chemical vapor deposition to a thickness of 314±1nanometers. The Si3N4 was deposited to create a core with a refractiveindex of 2.016±0.005 at a wavelength of 633 nanometers. The p-dopedsilicon wafer with the applied coating was then chemically andmechanically polished to create an average surface roughness of 4±0.8angstroms while creating a final core thickness of 286±1 nanometers.Identical coatings were applied to both sides of the wafer in order tobalance stresses, and therefore mitigate warping or bending of thewafer. These stresses are a result of the low-pressure chemical vapordeposition process.

In this example, a pair of upper electrodes were formed wherein eachelectrode had a plurality of refractive prism-like shapes in series,such as shown in FIG. 18. In particular for each electrode, ten (10)triangle elements were designed using an index modulation of 0.02,125-micron beam waist, and a constant triangle base size. Each electrodewas etched into the cover plate by standard photolithographictechniques. Specifically, standard masking and chemical etchingtechniques were used to pattern the ITO on the glass cover plate.

Table 2 below shows the coordinates of a 20-micron wide line ofdemarcation defining the space between the triangular shape electrodesfor this example (see also FIG. 18).

TABLE 2 Dimensions of 2 Electrodes X Dimension Y Dimension MicronsMicrons 0 250 1000 −261 2000 294 3000 −350 4000 428 5000 −528 6000 6507000 −794 8000 961 9000 −1150 10000 1361 11000 −1594 12000 1849 13000−2127 14000 2426 15000 −2748 16000 3092 17000 −3458 18000 3847 19000−4257 20000 4690

The wafer (having a conductive substrate, lower cladding, and core) wasdiced into smaller 20 millimeter by 40 millimeter parts. Each diced partwas then coated with an alignment film approximately 120 angstroms inthickness. The alignment film was used to create the homogeneousorientation of the liquid crystal upper cladding. The film was producedby spin coating an 8:1 mixture of Nissan polymide varnish solvent #21 toNissan polymide type 2170 filtered at 0.2 microns at 3000 revolutionsper minute.

The same spin coating process was performed on the cover plate (havingthe two upper electrodes). The glass cover was made of 1.1 millimeterthick 1737 corning glass coated on one side with an indium tin oxide(ITO) film to produce the 100 ohms/square conductive layer used for theupper electrodes.

Once both the wafer (with the lower cladding and core) and the coverglass (with the two upper electrodes) were coated, the polyimidecoatings were imidized by baking in an oven at 200 degrees Celsius forapproximately 1 hour. The polyimide coatings were mechanically buffedwith a dense piled cloth to induce preferential alignment along thelight wave propagation direction of the waveguide.

The cell, into which the liquid crystal upper cladding may be contained,was formed by spacing the cover plate (e.g., 1737 glass window) from thediced wafer parts with 5-micron borosilicate glass spacers immersed in aultra-violet curing adhesive Norland 68. On the bottom side of thecoverplate is the patterned electrode, in this example. Approximately500-micron dots of the spacing mixture were placed at the four cornersof the wafer (having the lower cladding and core) to create the cell gapfor the liquid crystal to be disposed therein. The cover plate wasattached to the wafer so as to create an anti-parallel alignment layeron the waveguide core and positioned such that the cover plate distaledge corresponding to the beam steerer output was aligned over thedistal output edge of the waveguide. The cell gap was then exposed to365 nanometer light until fully cured. Straight Norland 68 was used tobackfill, via capillary action, the remaining exposed edges making upthe cell gap. Two 3-millimeter openings were left, one on each oppositeside on the edges 90 degrees to the buff direction. MLC-6621 liquidcrystal, obtained from EMD Chemicals, Inc., was then introduced to oneof the two edge openings and allowed to fill the cell gap via capillaryforce. Once filled, the holes were plugged by using Norland UVS-91visible-uv curing adhesive. Once fully cured the output edge of theassembled device was polished utilizing diamond impregnated polishingpads supplied by Ultratec Manufacturing, and the final polish wasperformed using 0.2 micron diamond. Braided wires of AWG were thenattached to the two upper electrodes and one lower electrode usingconductive epoxy.

Operation of the waveguide included coupling 780 nanometer light intothe waveguide by means of a gadolinium gallium garnet GGS 30-60-90prism. TM light was introduced into the TM0 mode of the waveguide.

A simple switching circuit was used to selectively apply a voltage toelectrode 1 or electrode 2, (see FIG. 18 and Table 3). Amplitudemodulated 6 KHz square-wave drive voltages were applied to the selectedelectrode to change the index of refraction of the region of thewaveguide under the selected electrode. To measure the beam deflectionchange as a function of the applied voltage, a silicon CCD video camerawas used to visually map the scattered propagation streak within thewaveguide. The experimental results are shown in Table 3.

TABLE 3 Voltage Voltage Electrode #1 Electrode #2 Deviation Angle (RMSVolts) (RMS Volts) (Deg) 0 0 0 22 0 3.8 26 0 4.7 46 0 7 93 0 9.2 139 011.6 190 0 13 230 0 13.5 274 0 13.5 363 0 13.7 0 0 0 0 22 −3.4 0 26 −6.40 46 −6.9 0 93 −9.1 0 139 −10 0 190 −14.1 0 230 −14.8 0 274 −14.8 0 363−15

As shown in Table 3, approximately 28.7 total degrees of steering wasachieved in this example with an applied voltage of 363 volts RMS. For avoltage of 22 volts RMS, 7.2 total degrees of steering were realized.

Embodiments of the present invention may experience swapping of energybetween the fundamental TE and TM waveguide modes at a particular valueof applied voltage. As stated previously, for liquid-crystal molecularalignment parallel to the propagation direction of light, the effectiveindex for TM polarized light decreases as a voltage is applied and theeffective index of TE polarized light is unchanged. It is possible, forcertain waveguide designs, that at a particular value of the voltage theeffective indices of TM and TE polarized light will become equal. Inthis case the two modes are phase matched and energy can swap from theTM mode into the TE mode and visa versa. For devices with moleculesorthogonal to the light propagation vector, the TE index increases asthe TM index decreases and phase matching at a particular voltage canalso occur. In many applications it may be desired to avoid such TE andTM mode crossings.

In one example, TM/TE crossings may be avoided by increasing the indexof the guide layer. For planar optical waveguides with isotropiccladdings, the index for TE polarized light is preferably greater thanthe index for TM polarized light. Furthermore, an increase of the indexof the guide layer increases the separation between the indices for TEand TM polarized light. When the separation between the indices for TEand TM polarized light becomes substantially large compared to indexmodulation of the LC waveguide Δn, then TE and TM crossings are avoided.

An example of an LC waveguide without TE and TM crossings is an LCwaveguide with the guide layer replaced with a 0.58 micron layer ofsilicon nitride prepared by plasma-enhanced chemical vapor deposition.The refractive index of silicon nitride at a wavelength of 1.32 micronsis about 2.0. Other suitable guide layers include stoichiometric siliconnitride prepared by low-pressure chemical vapor deposition and titaniumpentoxide. A device of this design, with the LC molecules alignedperpendicular to the propagation vector, was shown to exhibit a tunablebirefringence (the difference between the TE index and the TM index) of0.035 at a wavelength of 1.32 microns, with no evidence of TE and TMcrossings. The modulation indices of TM and TE polarized light wereapproximately 0.02 and 0.015, respectively.

In some examples, nematic liquid crystals may be driven with a voltagesource with a very low DC component, such as an AC square wave. The fastresponse of the liquid-crystal molecules in proximity to the guide layercan lead to temporal transients in the modulation index of the LCwaveguide during the finite transition times of the square wave. In someexamples transients in the modulation index may not be desired. Sincethe fastest response times for the LC molecules can be associated withstrong molecular restoring forces and high operational voltages, oneexample of how to reduce the transients is to reduce the operationalvoltage. In Table 2, the transients operate in time scales of several10s of microseconds for operational voltages above 50 Vrms. For manyapplications it is also desirable to reduce the operational voltages inorder to simplify the driving electronics.

One example that may reduce the operational voltage is to reduce thepolar anchoring energy of the liquid-crystal molecules to the alignmentlayer. Alignment layers that produce homeotropic alignment have lowerpolar anchoring energies than for buffed polyimides that produce planaralignment. In the electrode example given above, approximately 70% ofthe total device stroke occurred below 50 Vrms. Other LC alignmentmethods known to have lower polar anchoring energies than buffedpolyimide include photo-aligned polyimides and polymers, angle-depositedSiO and SiO2, non-polar polymers, and the use of surfactant-modifiedliquid crystals.

A second method to reduce transients in the modulation index may be toincrease the frequency of the voltage source. The use of drivingfrequencies above 20 kHz at 50 Vrms often is aided by the use of liquidcrystal materials with very low conductivity or a large voltage-holdingratio. The liquid crystal MBBA exhibits a low conductivity as dosuperfluorinated liquid-crystal materials.

By combining the effects of reduced polar anchoring energy with a highdrive frequency, transients in the modulation index can generally bereduced to a desired or negligible level.

A way of achieving pure TE modulation is to use smectic A*liquid-crystal materials exhibiting the electroclinic effect. Thesematerials rotate about an axis containing the electric field vectorgiving pure TE modulation and leaving TM polarized light unaffected.This configuration has the benefits of low DC voltages, and completelyeliminates any possibility of transients in the modulation index.However, the modulation index may be less because the directorstypically switch less than 90°. Smectic A materials also tend to havemore restricted temperature ranges than nematic materials and theirdevelopment is less mature.

Accordingly, it can be seen that embodiments of the present inventionprovide for dynamic electronic control of light as it propagates throughthe waveguide. Embodiments of the present invention could bereplacements for widespread applications such as retail store barcodescanners, CD/DVD optical read/write heads, optical/holographicdatastorage, telecommunications optical switches, bio-sensing (i.e.,lab-on-a-chip) applications, optical computer backplanes, for example.In addition to the beam steerer applications, the tunable lens designscould permit electro-optic zoom lenses, selective detection forlab-on-a-chip biosensors, tunable collimation lenses for fiber towaveguide couplers, for example.

Embodiments of the present invention may be used in conjunction withconventional digital and analog circuitry, either separately orintegrated on a single integrated circuit. For instance, the voltageapplied to one or more patterned electrodes may be controlled by amicroprocessor or other logic or programmable logic devices, and suchlogic may be included on the same integrated circuit with the waveguide.

While the methods disclosed herein have been described and shown withreference to particular operations performed in a particular order, itwill be understood that these operations may be combined, sub-divided,or re-ordered to form equivalent methods without departing from theteachings of the present invention. Accordingly, unless specificallyindicated herein, the order and grouping of the operations is not alimitation of the present invention.

It should be appreciated that reference throughout this specification to“one embodiment” or “an embodiment” or “one example” or “an example”means that a particular feature, structure or characteristic describedin connection with the embodiment may be included, if desired, in atleast one embodiment of the present invention. Therefore, it should beappreciated that two or more references to “an embodiment” or “oneembodiment” or “an alternative embodiment” or “one example” or “anexample” in various portions of this specification are not necessarilyall referring to the same embodiment. Furthermore, the particularfeatures, structures or characteristics may be combined as desired inone or more embodiments of the invention.

Similarly, it should be appreciated that in the foregoing description ofexemplary embodiments of the invention, various features of theinvention are sometimes grouped together in a single embodiment, figure,or description thereof for the purpose of streamlining the disclosureand aiding in the understanding of one or more of the various inventiveaspects. This method of disclosure, however, is not to be interpreted asreflecting an intention that the claimed inventions require morefeatures than are expressly recited in each claim. Rather, as thefollowing claims reflect, inventive aspects lie in less than allfeatures of a single foregoing disclosed embodiment, and each embodimentdescribed herein may contain more than one inventive feature.

While the invention has been particularly shown and described withreference to various embodiments thereof, it will be understood by thoseskilled in the art that various other changes in the form and detailsmay be made without departing from the spirit and scope of theinvention.

1. A waveguide, comprising: a substantially planar core for guiding alight beam through the waveguide, wherein said planar core has athickness of less than one half a wavelength of the light beam, whereinthe core has an index of refraction sized such that a TE index is notequal to a TM index for an operable voltage range of 0 to 100 V to avoidTE and TM crossings; at least one cladding having a liquid crystalmaterial disposed therein; and means for controllably refracting thelight beam in a direction parallel to said planar core as the light beamtravels through the waveguide.
 2. The waveguide of claim 1, wherein themeans for controllably refracting includes: at least one electrode forreceiving at least one voltage, said electrode defines at least onerefractive shape; wherein the light beam is refracted by an amount thatis controlled by the at least one voltage.
 3. The waveguide of claim 1,wherein at least a portion of the liquid crystal material forms one ormore refractive shapes having an index of refraction; and the means forcontrollably refracting includes at least one electrode; wherein as avoltage is applied to said electrode, the index of refraction of the oneor more refractive shapes is altered to controllably refract the lightbeam as it travels through the waveguide.
 4. The waveguide of claim 1,wherein said cladding has a first region characterized by a first indexof refraction and a second region characterized by a second index ofrefraction; and wherein the means for controllably refracting includesat least one electrode; wherein at least the second index of refractionis controlled by a voltage applied to the electrode.
 5. The waveguide ofclaim 1, wherein said cladding has at least a first region that includesat least a portion of the liquid crystal material having a firstorientation; and the means for controllably refracting includes at leastone electrode; wherein the first orientation of the first portion of theliquid crystal material in the at least first region selectively changesfrom a first state to a second state based on a voltage applied to saidelectrode.
 6. The waveguide of claim 1, wherein the liquid crystalmaterial is comprised of a superfluorinated liquid crystal.
 7. Thewaveguide of claim 1, wherein the liquid crystal material has abirefringence greater than 0.1.
 8. The waveguide of claim 1, wherein thethickness of the planar core is sized such that the index of refractionof the waveguide changes by at least 0.01 over a range of 0 to 50 V.